If any part of Tai Hao's keycaps is POM, it's the portion that makes up the legends, but definitely not the main shell of the keycap. I've had a couple of Cherry G80-3000s with POM keycaps, and that material is very distinctive. There are also quite a few POM parts in the switchgear in my car, and all of it has the same distinctive slickness of POM keycaps. The main part of Tai Hao's keycaps is definitely PBT. It's also thin enough that I've seen some of their keycaps crack, including one of my own. I've always assumed that the plastic Tai Hao uses for the legends isn't PBT, because it's somewhat shinier. I used to have a set of their black on dark grey keycaps (the ones that mimic black Topre keycaps), and the legends were always slightly shiny, which made them even harder to read than they should have been.
Otherwise, I agree that Tai Hao makes decent keycaps for the price. I just ordered set of their doubleshot PBT keycaps for $40, and they're well worth that price. Even their doubleshot ABS keycaps aren't half bad. They're definitely a step or two above what comes on a Filco or a Das Keyboard, and some are as cheap as $19.99.