I've got a Multipede. It works exactly as advertised. Both games play near perfect (as far as I can tell). It's real nice to be able to easily switch between the two games. Guests really seem to like picking their favorite.
Personally, I thought the cost was a bit high. But I guess if one considers the time and effort, and the relatively few that would be sold, I guess it justified. But paying for a Millipede board and the $85 for the new ROMs definitely would be too steep for me.
One thing to consider: if you really want the original, authentic feel, then consider that you'll be using a 2 1/4" trackball to play Millipede, which had a 3" trackball. And if authentic feel is not a big issue for you, then should you put the money into a MAME machine? Only you can decide.
Hope I helped.
Mario