The good news is that it really did help with the staining.
The bad news is that my cup smells strongly of mint. I didn't think that the tabs would make it smell this much, and I'm not really worried about it being harmful, since silicone is non-porous, but it's just a little...disconcerting.
I washed it with soap and water and let it air out for about a week, but the smell is still there. Have any of you had similar experiences? Can anyone think of a reason why I shouldn't use this cup, given that I don't have strong chemical sensitivities and the cup seems totally fine?
If this isn't a problem, it might be a decent way to deal with cups that have developed an unpleasant smell.