I use the TG-5 for snorkeling only. For deep diving, you’d need something better, like one of the underwater cases available for almost all DSLR and mirrorless cameras, at prices rivaling the cameras that they are designed to protect.
In my youth, my father has bound a stone to a string and knotted the
string at every meter. He didn’t have a measuring tape with him, but
as a carpenter he damn well knew what a meter is. He may have been a
few centimeters off, no more.
Sitting in our boat he let the line down where I dived, and we
measured 12 meters. I’m pretty sure I can’t get that deep any more.
Last year I may not have been deeper than eight meters. No problem,
the camera is rated for 15 meters.
Is it fun? Well, yes and no. First of all it is very frustrating. Don’t even think about carefully composing. You can do that with an aqualung and a lead belt. Maybe. While snorkeling, you dive down, try to get to the point that you imagine would give you an interesting view, orient yourself, point the camera, click … and rise to the surface.
You really need to make up quality with quantity. It’s possible to get some usable pictures, but it is much harder than I hoped it would be.