I've used a number of the cheap disposable underwater cameras over the year but never liked the results. If I got 1 or 2 photos worth keeping I considered it a good day.
With the MPK-P9 and the Sony CyberShot DSC-P5 camera I can shoot away underwater and simply keep reshooting until I've got the image I want (mostly of my kids mugging for the camera underwater).
The MPK-P9 is REALLY solidly built. It has buttons that go thru the case and allow all of the controls of the camera to be operated underwater. Especially key are the flash on/off and zoom buttons as well as the review button to insure the shot worked.
So far it's kept the camera totally dry but I haven't tested it to the 40m. I've just gone snorkling with it.
The docs do warn quite a lot about keeping the gasket clean but an extra one is provided.
The major downside is that it is pretty heavy - understandable to survive 40m! Easily doubles the weight and size of the camera. It is slightly heavier than water near the surface so it slowly sinks. I would be preferred it to be the other way around and slightly boyant - just in case I drop it over the side in 300' of water.
One trick to remember is that when coming back out of the water you have insure the lens is clear of water drops or the photo is very blurry.
At only $99 direct from sonystyle.com it was a bargain.

Recommended: Yes