The lessons for new players, the hand of the day and the bid of the day are free, and there are no ads.
I'm Joe, and I make The Stayman Whisperer at Joywright Studio, a small studio that builds things with care and craft. Every card the app marks is checked by a double-dummy solver, and where it's a guess, judged by its chances over the layouts that fit what you know, so what it teaches you is right.
If it's helped your game, a tip helps keep the free side free. It pays for the servers and the solver's time, and for the time to write the next lessons.
Good luck at the table. Joe