Don't see the need for these out front Garmin mounting brackets ........ What else are you going to put on the stem ANYWAY? ;-)
There is a difference between need and want. No-one needs one (unless they have a very specific health issue which limits their neck mobility to within a very specific range), but some people want one, for various reasons. It is surprising how much it improves the visibility of the screen, it also makes it much easier to fiddle on the move as you can keep hold of the bars at the same time. Then there is the most important thing................ it looks better!
I cycled with a 500 on the stem for 3 years and didn't feel it was bad at all, but I now ride with an 810 out front, the out front position is great, I really like it and would not want to go back. The 810 however, well lets just say, it hasn't matured yet.