[Richsgt]

They might work out, the best way to check any gearbox is to well...open it up just like us FIRST'ers do with just about everything mechanical. From my experience a good robot gearbox shifts fast, can take a large side-load(from parts bending after repeated contact..or bad measuring), and don't need to be checked or fixed often.
To that extent unless ryobi has updated recently(which they might have, I'm not sure) they might be a little weak. They used to have plastic gears in the gearboxes, this was a few years ago but just open one up and check. I'd stick with dewalt as they use metal all over in the gearboxes and i own a dewalt drill thats never had a gearbox problem ever.
...Open it up anyways thats half the fun