This just seems like more crap to dangle off your rig. I’ve employed dropper posts for over thirteen years and the damage that this doohickey protects from has never happened to me. When I am hauling mail on a trail, my seat is down anyway. I lived through the time when there were a zillion plastic things you could bolt on a skateboard to “protect” it or give you better “performance”. If there is a way to make money off pointless shit someone will find it.
The problem I have with the inner tube is that I like to wipe the dust from the seatpost stanchion after every day of riding and give it a light film of silicone. A boot would make that unnecessarily time-consuming.