There's been a bit of discussion about PJB on this forum before, but i'll chime in with my experience.
I own a PJB Briefcase and it's my favourite amp for double bass. It has a very sweet (to my ear) sound, that is clear and present. I also have an EA iAmp500 and Whizzy 12, but I prefer the sound of the PJB.
Cons: It's quite a heavy amp for it's size and wattage. I'm thinking about upgrading to the Suitcase to get a bit more useable volume (the Briefcase can power an external cab as well, if you have a splitter cable or two outs on the back of your extension speaker).