I don't recommend these, for a few different reasons. The primary one being that it isn't hardwired to anything. It also isn't a slide lever I can use to manually apply the brakes, it's a button on a screen which is...not how the slide lever should work.
Then there's the issue of outside electrical interference. Don't get me wrong, bluetooth is pretty solid, until it isn't. For instance, there is an approximately 1-mile stretch of road near my home where the bluetooth connection between my truck and my phone (same happens in the wife's truck, as well as my FIL's truck) acts up, and sometimes fully disconnects for a few seconds. We have pinpointed where the area starts and stops, but we cannot figure out what causes it.
Now imagine you're in an area like that, and some outside electrical interference cuts your brake controller out, and you need to make an emergency manuever. Now you don't have trailer brakes - a dangerous situation when you have a big, heavy load behind you.
Is it far fetched for something like that to happen? I used to think so. But since we've discovered this 'dead zone' nearby that interferes with bluetooth, I don't think it's as far fetched anymore.