it's not currently on ebay. But you can get it from here
http://www.arcademvs.com/ARCADE_ACESSERIOR.htm
product a-22. The problem is this one's a bit stripped down so you have to know a little about wiring. But it's pretty straight forward. I wired it into a computer hdd power supply molex to get power. And just the rest is rgb in and s-video out. The composite video on it looks terrible. But the s-video is clear and nice. The only problem I had with the s-video was the chroma output was too high. Since there's only rgb adjustment pots on it I just added some resistors to the chroma wire of the s-video cable plugged into it and the picture became perfect.
As for compatibility it works on all my arcade pcbs, megadrive, and super famicom. Super famicom it needed a 100uf 10v capacitor on the sync line to get a working sync signal since it has extra voltage going through the lines on the ntsc models. Ironically the first system I ever hooked this board up to was a US genesis model 2. I just spliced up a scart cable and wired it straight into the encoder and it worked great.
component video is better looking but s-video's good enough for me and my tv doesn't have component jacks. I have a friend with a new astro city arcade cab running a brand new moniter he bought. Myself and other friends have played games on his cab and then played stuff on my setup and they all agree my setup's pretty darn close in picture quality (just very minor colour bleeding)