I have a MM5 for sale and I played a MM 4 at Sam Ashe yesterday. There is a huge difference in quality and sound. The 5 is much heavier and full sounding. The neck and the board have a much better feel to them and the bindings on the neck are night and day. To me, after playing the 5 for a while, the 4 just felt, sounded and looked like a copy bass. The slap sound is especially good and I tend not to use the preamp in order to get the old school sound. I don't play alot of slap-mostly fretless now so thus I must let the 5 go. I hope this helps!