I've got one
I installed tailbeaconX with an AV-30 in my RV-4. I'm happy with it and my cruise is about 165 to 168kts TAS. VNE is 182kts. No flutter issues up to 182.
One thing that is user interface related that I wasn't fond of in my plane is when I had the single AV30 I didn't have additional altimeter in my plane and when you need to flip transponder codes you must go to the page with strictly attitude indicator and I'm in busy airspace with low class B ceilings that I don't want to blow. In January I added a second AV30 so I no longer have this issue as I keep my data open on one AV30 and the other is where I set codes.
Only issue I've had is when using molex plug in the tail a wire came loose and there is no indication on the unit (showed good signal strength and all functionality still worked on unit interface) but ATC lost all contact with my aircraft other than "primary target". I was notified by tower when I came to land and connected with UavioniX who told me to check for loose connection. Their customer service has been excellent when I had any question about anything related to install or debugging.