I just tried it on my kids' Legos. I made two scans, one per box: it found ~2500 bricks, which I think is a very high hit rate. However, the build suggestions are very, very lacking. For reference, my kids are 8 and 4. The builds proposed are very simple, small, and still mention missing pieces (probably related to colors, which honestly most kids don't care about). I think my 8yo would like it, she tends to build "worlds", assembling many related contraption that each are fairly simple and match the themes found on suggestions.

As for my 4yo, forget it. He is a builder, making very elaborate and complex constructions, the bigger the better. He would find suggestions absolutely uninteresting. I didn't try to scan Technic legos (which he is fond of and make astonishingly complex contraption given his age). But it's an even more complex problem to solve.

I suspect work on the app was focused on recognition, which honestly is impressive. The second part, finding models, maybe need a bit of work ? I would recommend at least having an option to "ignore color": it's nice to have a build that looks good, but overall most kids - including myself - like to build first.