I use Clear Tune every day. It was one of if not the first full featured tuner app on the App Store. It's been updated regular and I've never had compatibility issues as iOS has been updated.
Driving in to teach in the mornings I set my iPhone in the dash mount and use the drone feature to buzz along. I usually do a little Stamp free lip routine in the car after the kids get dropped of at day care and Stamp #1 at the red lights. The tuner is great but I probably use the drone more. I don't do mouthpiece work with my kids a ton but when I do it's always with Clear Tune droning away.
Not much else to say...I like it, it's stable and it works great. If you need a tuner and run iOS get clear tune.
