Never used an in-tank UV...and i dont think I would ever try, as they would get covered in crap fast as they are passing unfiltered water over them.
I have always used inline UV filters that was the water they have going through them is as clean as possible, and i also have it flowing slow through the UV
I use GreenMachine from petsmart, works well IMO. 24w @ 100gph. Has a screen to keep debris out, has an indicator light on the12v adapter outside the tank for when it's operating correctly and bulbs last 4-6 months on average.