Have one, it's in the closet...
Remember that UV only affects WATERBORNE organisms. Most of the bacteria in your tank are benthic/demersal, so little benefit will be seen in that respect. If there are algae cells/spores in the water column, it may help, assuming you have the correct power and contact time for whatever you're tying to kill. Also realize that the UV unit will heat your water a bit.
A good skimmer would be a better investment, IMHO.