DS is 3yo, 34 pounds, not sure how tall now (maybe 38-39") and still uses it. We have the potty seat for the regular toilet but he still prefers the potty chair.

Honestly, by now I'd prefer he used the potty seat and step stool because I hate cleaning the potty chair now that he finally poops in the potty. But his legs still dangle from the regular toilet even with the step stool, so he prefers the potty chair.