Water spray from the props would be my biggest concern, and it looks like the water would need to be absolutely dead calm for this to be feasible at all. If it was salt water, I wouldn't even attempt it.
Definitely cool though - it would take me a while to trust a water landing. At least this way you don't lose your drone in the event of an emergency landing.
I have been flying my Mavic pro on my original prop float kit for nearly 2 years. Hundreds of water landings and never any water spray on the drone from prop wash.
In the several weeks I have been working with my similar but newly designed
Mavic 2 float kit on my
Mavic 2 I have not had an issue with water spray from the props.
They will handle 6 inch waves. I have actually watched them handle bigger than that from a boat wake. But you are right if you want to land your drone on water calm is better. I have used them for water launching/recovery from my kayak.
What you said about not loosing your drone in an emergency water landing is the whole point. if you run your battery to low and it goes into emergency land mode it can land and float safely on top of the water.
Most people just use them for piece of mind while flying over the water, never intending to land on it.
Even if it flips upside down it will continue to float so you can recover it. Of course it will be wet from being upside down in the water. If it is fresh water you can dry your drone out in a bucket with rice in it sitting in the sun over a couple of days. Your battery will not survive, but your SD card will so you can recover your data.
My Mavic Pro fell into the Dora canal after hitting a small branch an tumbling through a tree. Floated upside down and I recovered it, dried it out and it still flys great today.
I hate to admit it but I crashed my
Mavic 2 Pro into Lake Dora, flying fast too close to the water. It hit at about 20 mph which flipped it. It floated upside down for over 40 minutes until I could get a boat to recover it. 2 days later it was flying great again.
Mike