For what it's worth, a store owner who sells both Modulus and the Flea bass explained to me, Flea's endorsement ended because Modulus is producing the Fleabass and he didn't want the name on both. The FB4 is the Funk Unlimited, but the FU is just a good story.
Flea used his Alembic on BSSM (can be seen on Funky Monks) and One Hot Minute. His reason: the even volume across the neck and that it's 'not in your face like a MM' (better for recording).
He toured with Modulus because they withstand temp/humidity swings better than MM.