I did some snuba in Hawaii this summer. I was there with my non-diver buddy to be the best man in his wedding. I was diving as much as possible and he really wanted to try some diving.
We took the whole family on a snorkelling/party boat the day after the wedding, and they had a SNUBA operator there where you paid a bit extra and got to snuba while the rest of the folks snorkelled. So he and I went snuba-ing.
They had this float setup with one or two tanks in it and a hookah regulator setup. We each had a standard second stage and a 25 or so foot hose. There were five of us and a guide on scuba. We towed the surface float and tanks along by our hoses.
I found I was always pretty much straining to go deeper and tow the boat thingy. It was comfortable enough, but you had to watch to not get all tangled with the other people. Being all tied together with other folks was weird compared to real diving. My buddy, having only snorkelled, LOVED it. I can imagine that it would be super fun if it was the first time you breathed under water.
The guy who was our guide gave us a safety talk...real quick, a few hand signals, a few thoughts about compressed air, but really, there's a reason scuba cert classes take everything slower, and build step by step. I could see how if you were prone to freaking out, you could still really get hurt. A quick briefing, and 10 minutes later, you're blowing bubbles.
The guide claimed the organization had a flawless safety record. Everyone on our jaunt was really chill, though only two of us had dove before. All the non-divers loved it big time.
I would think as long as you were trained on the scuba concepts, or at least knew to never ever hold your breath, and if you're in calm water, it's relatively safe. Basically, I think it's a lightweight "resort" way to experience a taste of diving, but if you want to dive, you should learn to dive the proper way. For kids...well, I would have LOVED a snuba setup in my folks pool when I was a kid. The garden hose didn't work AT ALL
Hope that helps

Gregg
EDIT: Duh...meant to say too. They threw a few weights on us. And two of the people on my "dive" were pretty young guys. They did great and had a great time. One was a certified diver. I'd guess they were 14 tops.