One caveat -- the water intake valve must be closed and since not all PWC's come equipped, one may have to be installed. Then you have to protect against forgetting to open the valve (which provides cooling water to the engine and exhaust) before use.
I have towed mine at about 8.5 knots, about 30 yards back (staggered so they couldn't hit each other if they wanted to) without incident, but always had someone in the cockpit watching. Actually, there was one incident. Leaving the harbor, while going at my customary 6 knots (idle speed, but my boat is long enough that there is no wake, or at least less wake than most boats at 5 knots) past the sheriff's office, the Sheriff told me to slow down as my jet skis were kicking up their own pretty good wakes.
But never had them turn over or get tangled, etc. This magic thing does look like it wouldn't require a watch. Edit: I just looked at the price. $3,500 each, so $7K in total. Not worth it to me.