I'm not saying the product is bad, only that if it gets recognized or talked about as an "X killer" it will almost always fail deliver the specified "killing", and hence it's a "failure" in that regard. You also risk creating higher expectations than you can reasonably deliver.

So basically, announcing your product as or having people talk about your product as a killer of any sort, is mostly a bad thing, be it a good product or not. You want people to say "it's very good", not "it's an X-killer".

Or at least that is my experience and opinion on "X killer" as a branding-strategy.