Pop out floats were invented and developed by the US Coast Guard Rotary wing Development Unit in Elizabeth City, North Carolina. We had them installed on our HO3-Ss (S-51). We never had the reason or opportunity to use them but in the developmental stages they landed with the floats deployed and they also landed (but very gently) to test the immersion switches. Naturally, after landing they had to take off again but the landing and takeoff were conducted in a protected area with minimal wave action. If you recall I had posted on another thread my experiences with this type of helicopter and how easy it was to get into ground resonance when operating off of a pitching and rolling flight deck. If the landing were made in the open sea things would be very difficult especially on the 3-S because it had a three bladed rotorhead and tricycle landing gear which made it very unstable. I would think that it would be very difficult to takeoff once having landed with the floats deployed for the same reason the 3-S had difficulty in starting up on the flight deck. The reason (Please everybody, do not jump on me telling me there is no such thing) is gyroscopic precession. The wave action will cause the fuselage to pitch and roll while the blades are rotating. This differential of movement will introduce a perturbing force into the rotorhead and it will respond 90-degrees later. The next movement may be in a different direction causing the rotor to precess in a different direction. This could cause instability in the rotor system. I doubt if ground (water) resonance would come into play because of the flexible as opposed to a hard surface but it would make it difficult to maintain control.
All of this is IMHO