Can I replace a cutler hammer GFCB120 breaker, with a GFCB120cs breaker?
So, since I had questions for Eaton tech support anyway, I threw yours in with the mix, and their rep said that the "cs" suffix is simply for retail (plastic clamshell) packaging -- it's the exact same breaker either way.  (The clamshell is what you typically find at a big-box store, while your average supply house would likely dispense with it and just give you the "bare" breaker without a package.)