I ordered the MAS Super Nova in Jan. (from MAS Systems of course) along with an MVS 4-slot (from MD Gamesales).
The controllers are of an extremely high quality (seem just like being in the arcade, really). I don't really like the layout for the Neo Geo, 'cause it goes sorta like this:
ABC
XXD
It causes a lot of trouble in Last Blade 1&2 for me, as it doesn't really feel natural to play it this way.
If they do custom joysticks, and you only want it for a Neo Geo and not other Jamma games, see if they will lay the buttons out like this:
BCD
A
This is a "natural" Neo setup.
The other problem I had, that you will probably also have if you get an MVS 4 slot board, is the fact that it won't sync properly with your TV without a little modification. I called MAS to see if there may be something wrong with my Super Nova when it wouldn't sync up and the dude was extremely knowledgeable and kind. He informed me that because you can adjust signal strength and stuff (used technical terms) on an arcade monitor, the MVS was sending out a weak signal. He informed me that to fix this, all I had to do was jumper (solder a wire to both ends)a resistor and told me how to figure out which one it was. It's the resistor that sets the sync and corresponds to the pin on the JAMMA connection from the board for v sync. He offered to do this for me, free of charge, as long as I paid return shipping. Being an IT weenie, I decided to try it on my own and shell out another $200 if I fucked up. Took the board apart, jumpered the wire and BAM! I was in business! I played MS3, much to my detriment, as I was supposed to work the next day and I played WAY too late.
I am extremely happy with my purchase, although now, after playing it for a couple months, one of the audio connectors is popping out of the Super Nova box. Should be easy to fix, but I am being lazy.
One last thing, I found that when I got my SN the picture had too much "blue" to be appreciated. On the inside of the SN there is the RGB to NTSC conversion thing and there are nobs you can play with to adjust the color. So if you get yours and the color seems off, try playing around with these settings before messing with the color on your TV if you have your TV set the way you want it.
Mine also didn't take that long to arrive, maybe a week via UPS. (they're in California and I'm in Maryland... west coast-east coast).
If you have any more ??? about my experiences and my SN, I would be happy to answer them. I went this way as it was WAY cheaper than going the AES route and I don't have anywhere currently to place an arcade cabinet (when I leave the parents house you can bet your ASS I'm getting a Neo Geo cabinet!).