MFI pumps are generally more powerful than EFI pumps and MFI can be used on both. The accumulator shouldn't really be left in. It will cause trouble if your injectors leak even a little bit. The accumulator should bottom out at around 2bar pressure, so it won't really screw up the transient fuelling even though in theory the accumulator tries to maintain constant pressure and the EFI regulator tries to tune the pressure with MAP.