UV has several levels of kill rate depending on how you set it up, however it will only kill what goes through it. BB is not really free swimming, so BB is not a concern. If you are getting a benefit from algae, then that would be unusual, since many people get UVs specifically to kill algae.
Pros: depending on settings (strength and flow rate), aids on removal of bacteria, algae, viruses, protozoa, parasites. Improves water clarity if algae is removed.
Cons: requires a suitable pump, and sufficient filtration so that particles don't severely reduce effectiveness, costs money, bulb needs to be replaced periodically, can't be used when certain medications are in the water; not all parasites will end up in the UV; if flow rates are below the bacteria growth rate, the UV will slow down but not control an outbreak.
It's possible to use the same pump you have (for example from a sump), but since the UV has a much slower rate, you'll want to split off the volume some way (a tee might work) on the return. UV is much more effective if the intake has good filtration. As these organism are .1 to 10+ microns, you don't want 200 micron particles going through the UV to block UV light.
Here are a couple links that might help:
http://www.drsfostersmith.com/pic/article.cfm?aid=440
http://www.peteducation.com/article.cfm?c=16+2154&aid=2855