I have a UGF
on my 75 gallon, and have had them on pretty much every tank I have had over the last 30 years. I always use power heads, and keep the gravel depth down to about 1 inch. I also always use them in addition to some other sort of filtration, mostly HOBs. I use a Python to clean alternating halfs, every two or three weeks, when I do a 50% water change. I always make a point of pushing the Python down firmly to the UGF
plate, and holding it there while waiting for the cloud of debris to get sucked clear before lifting straight up and moving over to the next spot.
As a result (I believe), I do not build up much crud under the plates, if any. Last fall, I removed the fish for a few hours and pulled out all the gravel, and the plates. So I had a good look at what had built up over the previous 4 years...not much. (I tie my plants to the UGF
plates with fishing line so that they do not float away every time I clean the gravel, and I was in the mood to move the plants to new spots in the tank. Pulling the plates out of the tank makes re-tyeing (sp?) everything MUCH easier!)
I think UGFs can be a good additional form of filtration IF they are used with strong-enough power heads, are cleaned well, and do not have too much gravel. FYI, I have fancy goldfish, mostly plastic plants (sometimes I add floating real plants, but they usually just get eaten), and no driftwood.
If you decide to remove your plates, be sure to move your fish out of the tank first. There has been some concern that the removal of the plates might release dangerous gasses of some sort into the water. These gasses will dissipate, but your fish should not be exposed to them in the meantime... I am not sure if this is true, but why risk it?