I wouldn't hesitate to put it on a CV. First, an entry would have to be really bad to be worse than a big unexplained gap. Second, startups go under all the time and everyone understands that this is more likely than not. If anything a potential employer would realize this has given you a useful bit of experience (but of course you should be ready to talk about what you learned). The only way it could be negative is if it was widely known that the product failed due to poor engineering (assuming you are an engineer), but this doesn't seem to be the case here.