i have one of these, purchased from a previous woot-off a long time ago. Mine's blue and black, but aside from the cosmetic differences, looks absolutely identical.
These things are awesome. I have a fairly large diving pool at home and use it almost exclusively there. The kids go ape Gigli (2003) over it, even the 3-year-olds. Somehow, it never gets old, and even at 3mph, it's fun to be pulled around the water.
The scooter is actually pretty light without the very heavy battery. The battery goes inside the nose cone, and then there's a large plastic cover that slides into the main nose cavity, and it has a rubber seal to lock out the water. It can sometimes be difficult to pull this cover back off, so an air pump is included just to pump air thru a little threaded cap in the cover so that it slowly pops off. On top of this cover sits a hollow buoyancy tank with a threaded cover. This container fits perfectly under the nose cone. You can add various amounts of water to it to control buoyancy. Leave it empty and the scooter floats to the surface if you let it go. Fill it completely, and the scooter sinks if you let it go. You can also add just a little water to make it just stay in place wherever you are.
To move, just squeeze both triggers on the handles and the propeller starts spinning at one speed only - there's no variable controls. Let go of either button and it stops.
As long as the prop is submerged, there are no bubbles in your face. You just have to point the nose to where you want to go and it takes you. It's really fun.
I brought it to a couple huge resort pools and had even more fun. And then I brought it to the beach in mexico and used it to tow a chain of five of us on rafts out a few hundred feet. It worked flawlessly, though a bit slowly with five in tow. I've never used it to scuba, but I imagine it would work great.
Mine came with a larger battery charger that hums when it charges, and it's very slow, but once fully charged, the battery lasts quite a while. Looks like they upgraded to a simpler adapter for charging. When the battery dies, the propeller just stops. You can start it again wtih the buttons, but then it just stops again. It doesn't fade out slowly.
I highly recommend this - if you have a body of water to use it in, you won't be disappointed for 100 bucks.