I could certainly see a demand for it in countries where it is legal. I don't see it being of much use in the US. Criminals are generally stupid but I can't see them advertising what corner they are going to be on via an app. Though I have seen them advertise on craigs list.
Personally i think theres a lot worse things out there than weed that people put in there bodies everyday. Im not even talking about other illegal drugs. Alcohol, cigs, fast food, the list is endless. I dont even get high and i feel this way, dont wanna get into a whole legalize/ dont legalize conversation. Im just saying i think its a good app, if you can look up a place to buy alcohol and cigs why not weed from a legal doctor?