I've been playing Multi-versus-Multi for a lot of years (pretty much as described by Chris Rydal on his paradox webpage (
Chris's multi-versus-multi page). I find it very good, and not all that hard to remember, since I play multi 2
♦ myself. One great feature is you do not have to pass with good hands (avoids the deadly 2D-pass-pass! mentioned earlier). Another advantage is 2
♦-2
♥ showing the balanced hand, which allows advancer to pass when weak with hearts or he can bid 2
♠ to play.
I am surprised how often it goes 2
♦=x (a major, a three suiter, or 19-22 balanced), all pass when partner has diamonds. The multi=2
♦ bidders seem to be confused. If Responder passes with a weak hand (bad), opener often thinks responder has diamonds and wants to play 2
♦X. Opener and Responder need to figure out what responders pass of this double means or you will get a lot of surprizing gifts.
I greatly prefer multi-versus-multi, but grandover's methos isn't horrible.