Been using the U5 for over a year now...
Just wanted to update: This box is the **** man. So far this year (because of various technical difficulties) I have used the FC the Aptflex the Vektor and the Realist and what I am finding is that the U5 is what makes the sound, not the pick up...that is, all these pick ups have their personalities but the U5 is what makes any one of them sound great. I really don't care so much about pick ups anymore. Right now I am using a realist and thru the U5 it is so sweet, loud, no feedback no mud. The Aptflex which is real brite alone, thru the U5 is warm and fat, the FC just sounds great (too bad the connection keeps ****ing up)
Sometimes for small gigs I am tempted to disengage the U5 from the Focus and just bring the amp, when I do I am always disappointed in the flat 2 dimensional sound, which gets loud but not round.
I still wish they would put the electronics in a smaller package, but the size isn't a deal breaker for me (I already have such a small rig with the W10 and focus that its totally worth the extra schlep) The U5 is slightly bigger then the Focus and a bit heavier.
I am really surprised that it has not caught on here, people spend so much time trying to get a sound and the one piece of electronics that makes the most difference is out there.