some people do alright with a ugf in a fish only tank, but if you want any inverts or corals, they will be a problem, in fw they do keeep things clean by sucking the trash under the filter, but in sw they they pull the garbage down and trap it too, only problem is that by trapping it, you are creating a breeding grounds for nitrates, so they are not as good as one would think, and are more maintenance,
the best filtration for a sw tank is what is called the berlin system, it consists of plenty of lr(about 1.5 lbs per gallon), a 4 inch minimum sand bed, good circualtion(10 times your gallonage per hour), and a protein skimmer, believe it or not the lr and sand do the filtering for you, actually they do the cleaning for you, they remove(consume) the garbage and break it down into gases whch then bubble out of the system, instead fo pulling it down and hiding it
HTh