Has anyone used The FPV Booster for Vision + by Soloman Mobile Tech.? It's on the apple app store for $8.99 Was wondering if it worked well.

Yes, I have.  It actually works very well.  I've gotten the wifi to go as far out as 3,000 feet as opposed to 1,000 or whatever it was out of the box.  I also upgraded my antenna after watching a youtube video on it.  That helped as well, but I know for sure the app improved performance.

I had a 100% gain in fpv distance.
That was before I lost it because I could fly beyond my line of sight...