Liquipel were charging something like $600 and sent it back with a disclaimer saying it didn't make the phantom waterproof and then they refused to use their product on drones very shortly after. It never worked and was a flop.
In theory it could work. They open it up and coat all the electronics in their waterproof solution. You can send a phone away to them and they will open it up and soak it in their solution making it 100% waterproof. There are videos out there of homemade solutions that will waterproof esc's that will work fully submerged in salt water so in theory it can be at very least made water repellant but to make it 100% waterproof is 100 times harder