I won't say that UGF's are junk, because the OP has forbidden such talk. So I will instead extol the many virtues of the humble UGF.
First of all, the UGF pulls everything down into the gravel. We know that. Any fish waste, uneaten food, etc works it way down through the gravel where it remains between the plates and the bottom glass - where you don't have to look at it.
As all of this matter lays there under the gravel, it continues to decompose, giving you wonderfully large amounts of ammonia - a definite boon for your beneficial bacteria - they'll never starve! This will increase their numbers, of course increasing nitrite, but then the next benefit comes along... another bacteria colony thrives! Yay! These guys produce tons of Nitrates, and this is where you come in...
The increased Nitrates will cause you to do more water changing. If you do your water changes with a bucket, you get a free workout, saving on gym fees! Cool!
Eventually, you will decide to clean out the UGF. Now the real fun begins. Since the plates are below the gravel, you get to remove everything from the tank... well, maybe not everything - just the decorations and stuff that is on top of the gravel. What a wonderful way to re-arrange your tank!
You could remove everything, gravel included and rinse the gunk from it, depending on how long the UGF has been running. But wait, where is the bacterial filter? Oh yes, IN the gravel. So, if you work really fast, and don't kill off too many of the bacteria, nothing much happens. But, if something does happen to the bacteria, you get the opportunity to start cycling your tank all over again! And this time, you get to do it with your full load of fish! Woo-hoo! That's gonna be fun with a capital "F" !!!
Yes, the UGF is a wonderful invention. Inexpensive to own and operate, with no filter media to change. Who could ask for more?