Garmin Edge 530 - can it be used for tracking walks

I guess it could be that the vivoactive corrects distance with specific acelerometers that count steps and those metrics, whereas the edge is only relying on gps signal?

Make sure you turn auto-pause off. The Edge is tuned for cycling and as a consequence it will auto pause frequently and undercount the distance when walking. Even with this change it is likely that the lower speed of walking will lead to more inaccuracy on the Edge.

You could also try setting the Edge into "MTB" mode, I don't know if it will help, but since mountain biking is a lot slower than road cycling the tuning might be more appropriate for walking (just a guess.)

There are differences in tracking on the EDGE when using the default GPS tracking facilities. Alone the presumption that GPS drift is handled differently. And walking speed is usually not much faster than what GPS drift can be, which is something thats filtered out more since the presumed cycling speed is above 5km/h.
Perhaps someone with more knowledge can comment on these differences.

There is a good Hiking app on the IQ store called Hike2+ that I've used for walking.

I would install and use that...

The Edge has a built in fail in that it can't give you the correct distance while walking. It's intentionally like that from Garmin. It won't even track a mountain bike ride distance accurately without a speed sensor. The GPS track can be perfect. The distance will be short by 25%. They simply don't want us to be able to use one unit for more than one use. They want another $300 dollars from us. To prove this simply go on Garmin Connect and export that walk as a GPX file and then re-import it. The distance will then be correct. 

So why would a hiking handheld GPS be able to get the correct distance? Garmin does this on purpose so that you can't use the unit for anything except cycling. 

It's so tuned for cycling that it also gives you incorrect distance while mountain biking unless you use a speed sensor. Fail.