The real test for a reading app: how does he seem after?
The real test for any reading app or program isn't whether it says the right things, it's whether your son comes out of a session steadier and more willing to keep going, or smaller and more reluctant. That's the trust you're actually looking for: help that meets him where he is instead of quietly setting him back.
There's an easy way to check whether a reading app or program is actually helping your struggling reader: watch what he's like when the session ends. Steadier and willing to come back is a good sign. Smaller and reluctant is a signal worth trusting, whatever the progress screen says. Fit, not features, is what decides whether practice helps or hurts.
What's really happening
It makes sense to feel helpless here. You went looking for something that would give your son steady, trustworthy practice, and instead the sessions have turned glitchy and frustrating, right when he needs support he can rely on. What actually determines whether a program helps or hurts isn't its claims or its design, it's how well its demands match where he is right now. Practice that's mismatched doesn't just fail to move him forward. It can rehearse failure, over and over, and quietly wear down his willingness to keep trying. That's why how he seems after a session tells you more than any dashboard does. A progress screen can say he completed a level. It can't tell you whether he left the table feeling capable or feeling small.
Tonight you can
Sit in on one session and watch his shoulders, not the page. Steadier or smaller, that's your answer. You don't need to analyze the app's method or compare it to anything else. You just need to notice him.
Keep practice short, and end it on something that felt like a win to him, even if the program had more queued up. You're allowed to stop before the app says stop. Ending on a note that felt good to him matters more than finishing what's scheduled.
Ask him afterward what felt easy today. It's a small question, but it tells you how the fit is landing from his side, not just from the program's side. His answer is information you can't get any other way.
What not to worry about
Being this careful about what you hand him isn't overprotective. It's exactly the judgment his reading needs from you right now. Paying close attention to fit, and being willing to pull back or switch course, is you doing your job well, not you being anxious or fussy about it.