Great looking tank.
If I were you I would look into maybe some foreground plants? Your choice, I think it would look good though.
About the filter, I have never had a U2, I do however have a U1 (I guess they're pretty much the same apart from size) down at the local school in the tank which I sort of manage there. Honestly I think its dreadful, It designed for 50 or so litres and it can't cope with 35, the flow slows down after about a day (Low stocking) I had to add another filter. I believe the reason for its badness is that the hole that the water flows through just after the sponge (about 2cm diameter) is directly touching the sponge, meaning that all the crud concentrates by the hole, meaning it gets blocked very quickly. I have a 2+ in my 40 litre tank and I can't fault it, apart from maybe the strong flow which moves the sand around a load, thats just me being picky though. I got it new for 17GPB from ebay.
Nice tank though, whats the lighting? Just out of interest.