I've owned most pickups including the Wilson, Barbera Realist, et all.
While I'm an endorser for Barbera I've switched to the Full Circle. It's a piezo and has it's set of limitations, but I think it's the best. I might like the Barbera as much, but not more. Problem with the Barbera is that I got tired of sending the bridges back for repair.
One huge thing that Phil had mentioned. People act like the FC is just throw it on the bass and all is good. I've found the FC to be EXTREMELY sensitive to all areas of setup. Like Phil said the surface that the piezo is against has to be making perfect contact all the way around. If your bridge is leaning a bit forward or backward can seriously affect the sound. I know because on my EUB (Volante) I put the bridge and pickup on and remove it on each gig. The Volante is cool because you can (carefully) adjust the sound post with tension on the bass. Really is educating as far as seeing immediately how small changes in the soundpost placement affects sound. Sorry, I digress.With the Volante I can really tell where the sweet spot is for the FC. And it is small. If the bridge leans a bit too forward or back it takes the tension off one sine of the FC. And you can hear it. By the way, Toby Timber's new mic/pickup mates really well with the FC. Very symbiotic combination. More front end thump and attack. A bit more natural sound. But only with the Doubler.(just kidding)