My father had a undergravel filter on his tank, this is years ago btw, and from what I saw, never had a issue and seems to be actually a pretty good system to have, but the only thing I would mention is that I think this works better with gravel type substrate rather than sand, especially fine sand as this clogs up the holes in the UGF base plate.
I am a fan of HoB filters tbh, had a C3 and Marina S15 and S20 on several tanks, chucked out the cartridges that came with the Marina filters and stuffed with sponge media and ceramics in a mesh bag and filter floss etc, did the job marvellously and access for pretty easy maintenance as well.
But for larger filter media and more water flow turnover then externals are hard to beat, especially good for overstocked or for large tanks, a bit more cumbersome for maintenance but plus side is only need to do this either every 2 weeks if overstocked or heavy bio load livestocks or once a month if normally stocked imho.