I recently finished reading the avionics satisfaction survey report in the December 2023 issue of Aviation Consumer, and while the thrust of the article is correct, I believe you missed two critical points.
Picking a shop to do the installation does not buy you future support. It all depends on the product vendor, and if they will continue to allow that shop to be in their network. My GPS navigator was installed by a good shop and worked perfectly the first time out. But the next year they did not sell enough units, so they lost their dealership and I had to go to a second shop for some upgrades.