I saw this at CES last week and it really works. Cost about $20 for a bottle that would be enough to do most radio equipment. Its done by immersing the object, inside and out and the resulting skin repels water.
My impression is there will be a re-treatment necessity with time. Also mechanical parts where there is wear will not be 100% waterproof.
The problem I can see is on a servo. You would need to coat the inside of the motors and if they were comutator types this would not last.
Brushless motors would be fine and an outrunner could be easily treated, so the problem of magnet damage on externally mounted submarine brushless motors could be avoided.