Complete reset

When you do the reset from the watch menu, make sure you select the erase data and settings option. Yes it is a good idea to remove the watch from Garmin Connect and Garmin.com (if it hasn’t already gone from the Products page of your account). However, before you remove it from Garmin Connect you can ‘disassociate’ ant CIQ apps in Garmin Express (can’t do it in GCM sadly); if you view the CIQ apps in Express (Watch needs to be connected by USB) there is an option to “Delete from List” when you right click on an unistalled CIQ app.

I'm not sure you can completely "factory reset" everything.
My firmware stays on 5.10, BT and GPS drivers are already updated and there is still music in the music folder when attached to the computer.

If it's leaving music, what other files and code is not being deleted?

I'm asking the same question: How do you return the device to exact "factory settings" with original firmware, no maps installed, etc?

How do you return the device to exact "factory settings" with original firmware, no maps installed, etc?

If you didn't take a backup after buying it, I don't think that's possible. You can erase all data from the internal memory, but this will also delete the preinstalled maps. Maybe you can delete everything BUT the maps (gmap*.*). It should recreate the other files and directories from scratch. Maybe leave the other *gma files as well as these are usually authorisation files, maybe for the preinstalled maps or other features.

Can you format the disk that is viewable in explorer when connecting the watch in Windows? Or will this brick it? :)

Can you format the disk that is viewable in explorer when connecting the watch in Windows? Or will this brick it? :)

No, that's not actually a "disk". The watch uses MTP so you can't access the internal storage directly (and format it). You can only delete files/directories.

Yeah, I'm wondering if erasing all those files you can access would brick the watch? I'd be worried there is some permission file in there somewhere.

On the Fenix 5 you could format the visible USB drive and do a button master reset and the watch would slowly rebuild the baseline file structure from data in some hidden area (I don’t recommend you do this with a Feinix 5 though). Whilst I’m sure much of the Fenix 5 Plus file structure would ‘restore’ itself in a similar way, if you delete the map files I believe they’re gone for good. Bottom line is I wouldn’t recommend wiping the whole file structure (recognising format is not the done thing for MTP). What I have found is that deleting the music and podcast folders is fairly benign, you just have to reload the music using Express after.

So, removing everything custom from Garmin Express (all custom faces, widgets etc), removing the MUSIC and PODCAST folders and then doing a master reset should in theory make the watch a factory reset unit with nothing that I have may have created/downloaded on the watch anymore?

In theory, yes.

Just remember not to delete the maps as they will not be automatically restored by the watch