I can't comment on the Garmin, but what I can recommend is the
70 Mai Dashcam Pro with the GPS module. It set me back around R1700 after shipping and taxes. There are some quirks, but overall I am happy with it. I am also going the route of fuse tapping so all the cables are hidden.
The main thing that swung me towards that cam was the fact that it didn't rely on a traditional mount (a really budget cheapy I had put me off these). This one sticks onto the windscreen (almost) directly, and I have it hidden behind the rear view mirror. The reviews were also pretty great. I had my doubts (because chinese), but I am really impressed with the quality of everything. Even the box looked and felt a bit posh. 70Mai is also a Xiaomi subsidiary.
@killerbyte can also vouch for this cam, as I showed him the footage and that convinced him to buy one too
Just understand that this cam, and the garmin (I think?), doesn't record what's happening at the back, so you wouldn't capture rear ends (unless you are the rear ender).