Uv sterilisation helps keep the bacterial count down - so therefore reduces chances of sickness etc
I'm not sure about its affect on paracites. If I was keeping delicate fish I would consider it from a germ killing point of view.
As for algae control, I'm sure it only affects green water type algae. The rest it doesnt affect.
I've been looking at adding this to my community tank now tat I have added 2 dwarf cichlids. Just to keep the water better as they are sensitive. I also know of other discus keepers who use UV sterilisers in their discus set ups for the sterilisation benefits.
I've looked around and you can get a small JBL one for about £30. (the 5watt version)