I don't really have an opinion on your question, but I'd point out that the relevant question to your business isn't whether it's reasonable for people to cover

I don't really have an opinion on your question, but I'd point out that the relevant question to your business isn't whether it's reasonable for people to cover their camera, but whether you can convince people it's worth purchasing something to use to do so. I could see that being an uphill battle since a Post-It would work, is free, and is less likely to make most feel like they might be judged as a paranoiac ... or conspicuously like they have something sufficiently unusual to hide that they need to purchase something that most people don't. (Not saying that makes logical sense, just that it makes "marketing sense".)