I addressed that. You should read a book to learn the definition of intervals. But in addition, there's no substitute for ear training. Grinding on interval identification is just as valid as this. Once you get to a level where you can identify intervals on the keyboard, the skills are pretty transferable. But there's just no way to learn what a fifth sounds like by reading a book. You need something like this. There is probably room to add a mode that says "this is a fifth" after you identify a fifth. Or to choose a named interval or chord quality based on hearing it. But I don't think any of that diminishes the utility of what's here.

FWIW I think it's probably more useful to play what you hear than it is to be able to name it. Although they're both good.

Right, and I addressed all that as well. I doubt we are in serious disagreement here and calls for me to “read a book” are frankly rude. I think you need to be more generous in the interpretation of others words because I actually disagree with the original poster for the most part, but you obviously have a different definition of “teach” than he. Flash cards don’t teach. They assist memorization or practice. Memorizing times tables doesn’t teach multiplication except trivially for the numbers you’ve memorized. It does assist in learning multiplication. Likewise this ear training can trivialize learning and identifying intervals later but is not itself “teaching intervals”.