It's not a bad idea, and I guess it depends on how much you would have to pay. Although I can imagine that the engagement of 'bought' users is less, there is also something called social proof. If your app attracts 1000 new users in the first day/week it must be worth it, right?
As far as ethics go, I don't object to these kind of things. It would be disturbing if you'd pay users for good reviews in the app store (which does happen), but paying for new users which will maybe leave a review in the app store, wether good or bad, is OK in my book.
As far as ethics go, I don't object to these kind of things. It would be disturbing if you'd pay users for good reviews in the app store (which does happen), but paying for new users which will maybe leave a review in the app store, wether good or bad, is OK in my book.