Recently I upgraded to the P5100 with the Fantasea housing. Although I have only managed (lousy weather) two dives with it, I've dry fiddled quite a bit, with and without the housing. Also, because I am forever timing out, I have had to do it as attachments. See below (hope this works).
Hi Reefhugger, Here is our response to your very nice mail (in bold italics) from Fantasea Line
Fantasea Line housings, accessories and water sports cameras
Fantasea Housing
Fits Nikon P5000/P5100 - Sturdy, all functions, compact, and threaded lens port.
I have several problems with this housing. However, at least this one could be peculiar to me. I find the spring loading of the shutter release button to be a little too much. As I hand hold/aim my strobe with my left hand, I shoot one handed with the right. The effort required to depress the shutter release is then, for me, almost built in hand movement, affecting sharpness and framing.
This is actually how most housings are designed, in order to allow for a 200+ Ft. depth rating there must be ample spring strength to resist pressure at these depths. We are confident that you can get used to this slight increase in spring strength.
Another problem is, where to place thumb. I have been putting it between the control wheel knob and the buttons for the four way switch. As I shoot in manual, there is some risk of inadvertently changing my speed or aperture. Another option would be, the thumb underneath and the middle finger for the shutter release. This then is a work in progress. However, I can imagine that this could be an issue for heavily gloved hands. I am fortunate, I dive in warm waters.
We have tested this housing and have found no problem what so ever with the thumb placement, either between the command control and multi function control or below it. Even with gloved hands.
Still another. The back cover has a rubber rectangle strip that presses on the camera and holds it in place. Unfortunately, this strip runs right over the focus light indicator. I have not yet done it, but I can see where I will have to cut out a 1/8” gap.
The rubber rectangle is in fact an anti glare hood which allows for better viewing in high ambient light. We can see no way it will affect the focus light indicator?
This one is a grouse. As economical as this housing is, surely we could have gotten a lens cap?
A reasonable gripe and we will look into it. But like you said, the housing is very economically priced.
And now a quirk. There is a little wishbone that fits over the telephoto lever. When you set up, the wishbone can press on the telephoto lever ever so slightly. The result is when you turn on, the telephoto (quite sensitive) runs right up to max, caught me out a couple times. After setting up, play with the telephoto a little and every thing settles down just fine.
This part has been redesigned and no longer causes even the slightest problem.
After all of the above, you would think that I am dreadfully unhappy with this housing. Not quite, if anything, I am satisfied. Some things to work out, yes, but the saving on the
cost of housing can buy a wide angle wet lens. For me, the threaded lens port is a big plus. And finally, so far it has not leaked a drop.
and you forgot to mention the free Flood insurance policy it comes with 
