When I was spear fishing, regularly, I used to shave arms, legs, and chest. Okay, I guess that's just about everything. Made it easier (and less painful) to get in and out of my wetsuit. I used a de after my shower. I would just wet the extremity, lather it up, and shave it. It's easy once you get all the long hair off to maintain. You've got to be careful around your knees and elbows.

Now, as far as your area below the belt, I would not recommend a de. You really need a flat surface. I would personally get a disposable with a pivoting head. Ymmv.