I agree with diver-hloc.
I still remembered that i bought a disposable underwater camera when i did my open water years ago.
My aim was to take picture of myself and the group underwater and maybe some fishes
I guess it serve it's purpose then. It gives me pictures and it was cheap.
I will never use those any more coz i don't wan just any pictures. I wan good pictures.
So i guess it really depends on your needs.