I don't think Wingly would ever 'harm' the income from flight schools. If you want a trial flight, where you yourself can take the controls of a real plane, then you're going to book through the flight school. If you want to go on a quick jaunt around the local area, and are happy to just do some sightseeing, then you pay half the price and go up with Wingly. You may then decide you enjoyed that flight, so you book a proper trial flight and get hooked, then complete your training with that school.
The way I see it potentially happening is that Mr Passenger wants to see if he's comfortable in a light aircraft without it costing him £200 (rough price for an hour's trial flight). Instead, he spends £50 on Wingly and decides he loves it. He then goes on to purchase lessons, which he never would have done if he didn't get the Wingly flight.
I agree with Jonzarno, there could be a few people out of the hundreds or thousands that use it, that decide to break the law. In this instance, as suggested, the authorities would find out and act appropriately. If, however, the majority of people use it as they should (which they will/do), then where's the problem? It's almost like saying nobody should own a car that can go above 70mph, as it facilitates them breaking the law on a motorway... Just because a few people do, doesn't mean that nobody should be able to own a car with a 150mph top speed...