I mean I am an expert in this sort of thing and I agree this is kind of a dumb idea. The innovation here is not the production of a color changing indicator, but rather putting it in a temporary tattoo. The indicator has existed for some time, and is well studied. The temporary tattoo thing is cool, but I question whether the additional cost and complexity of using it this way is worth it over existing technology, such as paper test strips. The criticism that it only tests for a specific, not commonly used drug is also valid because even though it is complicated to make something that tests for multiple drugs is far more complicated, not testing for the most commonly used drugs can create a false sense of security. It's like if you went to a big concert and security was outside only checking for swords and knives and not guns. Yeah those things are also dangerous but it's not the biggest threat. To further the analogy, imagine if a decent subset of people believed the security guards were checking for guns but weren't. That would be pretty bad right? I can't imagine the anti date rape temporary tattoo wouldn't be misunderstood to test for a wide variety of drugs or at the very least the most common ones by at least a decent chunk of people trying to use it.