I agree with Makalu, check out the Funky Monks DVD for the basses he used. There looked like an Alembic at times, a Wal at times and definitely used a MM5 on one track. I never got my hands on a Modulus Flea or a Flea bass but I'd love to take one for a cruise. Flea hooked up with Modulus after Dave Navarro joined RHCP because Dave was playing Modulus strat styles at the time. He openly hated anything strat like in look or tone in one interview I read back then. Dave never wanted to go after the Fruiscante tone, not because anything personal that I remember, but just that Dave was much more of a PRS type guy. Flea latched on for, as stated by Limeman, the ease of playing in different environments. I don't claim to be an expert but that was my 15 yr old memories of articles I read, feel free to correct me.