Would you buy a Fenix 6?

Right now you can get a Fenix 5 Plus off Amazon for $470; I'd go that route instead.  I have a Forerunner 945 which has the same hardware as the 6, and it's a bit of a train wreck right now.  The 5 Plus is rock solid with more tried and true hardware. 

Yes, if you read this forum , you can see, that there are almost no part of the fenix 6 series , which would work correctly. For me and others the stress level doesn't work, for others the OHR, the altimeter, the barometer, the GPS. So if you have luck, for you the needed watch parts will work :) The fenix 5x plus is even worse (I had it before fenix 6x pro)

GPS - If you are a road runner/biker, it is very accurate.  For twisty trails, I highly, highly recommend Stryd.
VO2 max - appears to be accurate.
Body battery - very cool.  It feels accurate.
Other - Bigger screen.  I may seem minor on paper but coming from a 5x+ to a 6xPro Solar, it makes a big difference.
The widgets are awesome.
The training features like PacePro is awesome.
There are so many great features and the processor is fast.
I love the maps as well.
People on here complain about the HR but mine and others have been really accurate compared to my Rhythm and Wahoo straps.
I think you chances are low that you will get a dud.
I politely disagree with getting the 5x+ instead.  I love the 6 over the 5 even though both are great watches.  Well worth the money and if you are considering the 6xPro, you have probably already budgeted accordingly if the value is there.
I encourage you not to be put off by those that have been soured by their experience.  It is a fantastic watch.

Big time thumbs up if the funds are available.

Big screen and map are definitely a great plus with this watch. Without them, maybe I would switch to Coros. 
then for the other points, my opinion : 

• GPS is okayish, but don't expect the best performances. Suunto is quite similar, Coros is better. Other watches from Garmin seem to do better sometimes. That's clearly one of the points to consider with the 6X. I'm using a Stryd to get a more accurate distance, because i'ts difficult to have some really reliable numbers otherwise. When cycling, it's much better.
• OHR can be really fine, but it's like the GPS : in some cases, it's not good. Most watches of this size will be like that : Suunto, Coros, same. It can be really fine, but also really bad. I use it sometimes, but in most cases, I use an optical arm band. It's a nice backup, but don't rely on it (especially on the bike, it can be pretty bad)
• VO2max, recovery, body battery, I think it's not bad ! It's the kind of metrics that is quite difficult to estimate, it's surely not perfect (even applications dedicated to recovery with HRV are not always reliable...), but I look at it, with the stress indicator also. It's something to balance with your simple common sense, as it's not perfect. But if someone can show me one watch or app doing significantly better without being less user friendly to use, I would be interested. Garmin isn't doing too bad on that.
• All day HR, I find it quite fine too, even if people hiking or doing some more intensive activities without recording them as workouts complain about it. I record as soon as I want something reliable. I use 24/7 HR for the rest, and I can't complain about it. Sleep tracking was a joke until firmware 10.1, now I'm waiting to see if it's better. 
  
  

The key advantages making me keep it are the screen (without sapphire, it's a pleasure to look at, big, great under the sun), very detailed maps, notifications / music / payment are a nice plus, titane version is lightweight and more comfortable than the 5X, battery life is really great. 

Forums are the worst place to get a feel for a product, as they are always where people discuss problems, by design it's where people look for help for problems. As a result, all forums for ANY product always leave a biased view of any product. They're great for looking for help, but you need to cast your net wider for a true range of opinions. Check out some reviews (like DC Rainmaker, Desfit ActiveJR) of the ones you fancy. DC Rainmaker in particular always does good reviews.

Personally - apart from some minor niggles, mine works a charm. I do 50-80 miles a week, run always with a belt, and have no doubts about the accuracy of the data I receive. The training data, recovery stats, pace pro, climb pro and the ilk seem to return very accurate data for me - but I have 3 years of fitness data in the Garmin infrastructure for it to use.

I'm a trail/ultra runner so the maps are a MASSIVE draw to me. I added the UK Topo Light to get contours and more of-road info, and then converted a bunch of KML's to IMG to get an overlay map of public rights of way for trails.

One piece of advice is that anyone seriously exercising with any device has to get a HR strap. The cheapest HR strap is far better than the most expensive optical wrist, and with the HWM RUN you get a load of extra running sats as well. Some people complain about having to spend a little extra, but then some of these same people don't balk at spending £100-200 on shoes or other gear. Wrist HR is good for some activities and gets worse for others -dependent on the degree of wrist flexing. It's a bad place to put a sensor.

In this sort of range you're looking at 

Coros - good hardware, but the software side is a bit lacking - no web access to data
Polar - looks good on h/w and sw front - no maps though (I'd love a Vantage V with maps!)
Suunto - excellent hardware, software side is a bit of a mixed bag at the moment

I've had - VA3, F235, F5, F5x+ and now a 6 (my Garmin history) so I have a wide range of data in Garmin Connect to draw on :)

'Rock solid' is not how I would describe the 5 Plus. I owned two devices over two years and the HRM dropped below resting level at some point during most of my high-intensity training activities. After three months with the 6 Pro I haven't seen this happen once and I've overall been impressed with the stability, fit and finish of this device. The health metrics seem consistently reasonable on the 6 though I have not conducted any experiments with a reliable baseline. 

Coros, I agree, GPS is best of the class. Quite impressive. Battery is also great. But their performance metrics are not good yet, VO2max, recovery, it's still a work in progress. Some innovative new functions now, but otherwise it's less complete than Garmin and focusing on ease of use. 

Suunto, the battery life in watch mode is a problem for me. 4 days with Suunto 9 ? I can get 20 days with a Coros or Garmin... That's a serious issue for me. GPS is acceptable, but quite like Garmin, it's not as good as with the previous watches. The lack of web app is a problem, but their mobile app is possibly the best of all, it improved quite a lot, and it's really nice now. I prefer to use it rather than Garmin Connect or the Coros app. Their metrics are not as many as on Garmin, but it's quite solid. Less settings, easier to use. 

Didn't try the Grit X from Polar yet :-P 

Well, the F5X+ is a good watch, with maps, music etc... But since it's bigger and heavier, OHR is not as good, and the GPS can really misbehave. At least on the 6X, it's more consistent. The smaller screen is also not as confortable. If you have the money for the 6, go for it. 

Im wearing the Fenix 6 (non Plus or so) since yesterday. 450€ at a discounter.

- its big and heavy
- the screen is OK. I dosent understand why a device for this price dosent have a brightness sensor. These manual On and Off for Background light are stupid

- the GPS?  Great. Im happy with it
- Body Battery? Just a question. Who can a body battery be correct when the device is not able to detect naps?
- i gues sthes Garmin boys havent heard about things on a Smartphone like "Widgets" or so. If you sync your System in the morning and open it in the eveni8ng - you can have take 10.000 steps. It will show you 100 from the morning, because it dosent sync in between.

So much funktions like haemeglobin who i dont understand.
The Instict also have correct stats, but no VO2 and a very cheap display.

In my eyes. Garmin sells a lot of cheap hardware for Highend prices. Irreplaceable and worth is that Dashboard/Webfrontend. Its great.

That's a lot of criticism, but I think Garmin is, in parts,  worth it. At least in price up to 500€. Anything over that, I feel like a rip-off.
On the other hand, you have an "Instinct" that costs 360€, but looks like a 5€ Chinese watch.

Hexxer said:

Body Battery? Just a question. Who can a body battery be correct when the device is not able to detect naps?

Just to answer this one point - the sleep detection has no impact on body battery so it doesn’t matter that the watch can not identify a nap. The body battery looks at the heart rate variability (HRV) which is represented on the watch as “Stress” and either “charges” or “discharges” based on that measurement. 

and for the original poster, I love my F6 Sapphire and would have no concerns buying it again. It isn’t perfect and occasionally does something stupid, but it meets my personal needs in the way I use it.