It's 100% safe as long as there are no other devices listed in the beggining.
I have a GT-S5660M (Canadian model and carrier) and I've tried ROM Manager while running both stock and CM. It never lists my device, just the ones that s!mon listed....
1. Flash the CWM linked from the ArpegGioMod first post with Odin. The one modified by Peteragent5.
I've been lurking on the forums for over a week now, reading tons of stuff, and learning all I can about my new Android phone....