We’re talking gimmick/toy vs basic research tool. You won’t be limited by what’s more or less a low end webcam with a cheap plastic macro zoom lens in front because you’ll have higher quality optics you can use with your eyes. You don’t run the risk of it not working anymore with newer hardware/software. If there’s ever a science project from school or the child is interested in science later on, a proper microscope will still work in 10 or more years, and you’ll be able to upgrade stuff.

You might need to buy used though although the stuff from Amscope and similar companies can be quite cheap while it’s new. Depends on what features you want.

For looking at teeth you’ll want a stereomicroscope which is cool because you can just throw stuff on the stage and look at it like it is and you get a 3D image. It doesn’t have the high magnification of compound microscopes though. Of course if you invest more you can also get good digital microscopes but for $50 it’s not gonna be great.