I love the idea of P/Js, but despite lots of experimentation in practice and rehearsal, in live and recording situations I always end up using the P-PUP only. It's perhaps a function of the music I play and the ideal sound in my head of course, but I find the back J-PUP far more useful when it can be blended with another J-PUP than when blended with a P-PUP. Only exception for me has been on fretless perhaps, when a solo'd back J-PUP can come into its own (all my opinion of course).