Yeah, SMS Rastan is a neat game, though fairly tough like the arcade original. I do like that the regions that didn't get the FM hardware still have the FM sound embedded in the ROM of each game, so you can still take advantage of that feature.
Now if only Rastan was fully compatible with Genesis controllers... The SMS controller's weird d-pad is doing me no favors.
I remember learning that non-JP region SMS games and trying to track down a Japanese Master System, just to hear this locked away sound. Let's just say I'm glad I have the Power Base Mini FM, instead, even if it took a long while.