I slap a lot with Evah P weichs on my little old German bass with a Full Circle, and I'm very happy with the sound. I can't say I swear by it, though...I swear at it when I plug in and there's no sound until I mess around with the jack a bit! It was less than a year old when this started happening, though unfortunately I didn't think to call Fishman about the problem until longer than a year after I purchased it, so they wouldn't do anything for me and if I recall, it would have been like 2 weeks turn around to have them fix it and they would have charged me $50. I took some pliers and performed some precision squeezing, and no problems since. So not the most durable, but I like the sound for slapping and regular playing.
Here's some vid of me slapping on it (and if you make it to 30 minutes, our bud Eugene from Gogol Bordello joins us for a few tunes). Caveat, I'm playing through the house Peavey TKO! Not really a rockabilly player either, but I get my slap on when I can!!! http://www.ustream.tv/recorded/18401197