I never use undergravel filters for many reason.
-They are a huge pain to clean.
-You have to have those things sticking out of them, they look ugly because of it.
-Can't have them in planted aquariums.
-I use sand for all my tanks, so it wouldn't work anyways.
-Gravel gets dirty looking aswell since everything sucks through it.
-Require an airpump.
-Don't work very well anyways, compared to every other filter.
-If you get an undergravel filter, you might aswell just get a sponge filter instead.
-They don't compare at all with Canister or HOB
PowerFilters, if you need more filteration, get a bigger filter.
Those are my reasons, that I can think of at the moment, why I would never use a undergravel filter.