As you can see, it was originally made by the folks at Direct Dutch (a language school). Overall the concept is a pretty good one. I’ve heard time and time again that Dutch people will switch to English at the first opportunity if they think you are not a native Dutch speaker. They do it for two reasons: they like speaking English, and they want to help you out. Of course, that is a generalization!
The one thing I have against the button is the language used: Spreek Nederlands! Met mij! = Speak Dutch! With me! In both languages it sounds very… forward, commanding and slightly rude. It would be better to remove the exclamation points and add a “hoor” after. That word does not have a direct translation in English, but it conveys a friendly tone. Spreek Nederlands met mij, hoor.
Time will tell if they make a slightly more friendly version 2.