I just went and bought a new Fluval U3 today to replace my Fluval U2 (bought second hand) as the out put flow was not as powerful as I wanted. I used the U2 in a 105 litre tank, I would go for the U3 it's not that much bigger,it has a much more powerful flow out put and lots of space for media, I don't use the included fine filter/ carbon pads, I just cut to size a fine filter from an external or pond filter and slot it in the cartridge after the coarse filter pad, it would cost so much to keep replacing the fine/carbon filter, these do need to be replaced every 6 weeks as the carbon will start leaking out all the junk it took out of the water, so as I as said above cut your own fine filter.We use an ehiem pro II 2028 on our 5ft tank but cause these ones are smaller we're using internals.
How do you rate the U series? We have been looking at these also.