Well! It came yesterday! Quite a coincindence. Had a lot of problems with it though.
1. Garou Densetsu takes a long time to load, doesn't it? Wait, no it's not loading at all.
2. Reposition card. Take ages to even get the CD-ROM screen working again. Maybe it's not that.
3. Try Saphire. This is taking a long time.
4. Try Saphire without the card in. Same screen. Looks like it's not recognising the card.
5. Panic a bit when I think I've bought a Super rather than Arcade card. Come to my senses.
6. Try Saphire again, and finally get a loading screen. Decide the intro is decidedly post modern
7. Game starts and looks a bit the same. Realise there should have been something in the boxes in the intro, so something's still not working
8. Try Garou Densetsu again, which works. However, it's not very good, and Mai's boobs don't jiggle.
So... as far as it go, I hae a nearly-working Arcade Duo.