I don't have the utrak, but do have the happs.
U-trak: easier to mount on wood panel: drill hole as noted in
instructions and moust.
Happs: metal mounting plate is easiest way to mount to wood.
Both have two small holes on bottom, one for the light to shine through, the other to screw the light to the TB.
I prefer my happs (old school & highlip models) over my betson & wico TBs (I don't like my happs highball, but others here like it). But all are high quality arcade trackballs. I'll bet the u-trak is as good as the others, but I'm just going on what others say.
If looks matter to you, the metal mounting plate the the happ TB can look bad if you don't hide it (or hack a mount that doesn't use it). As for the u-trak, I don't like the look of the optional "trim flange", or at least the pics of it, but it's supposed to make mounting it easier. Again, that's just my opinion, and others here feel differently. You'll have to judge for yourself.