I would suspect (depending on your state, of course) that you could open yourself up for a warning for allowing passengers to ride back there while underway. I've heard of that happening before while people were outside the playpen while the boat was moving. I know we certainly wouldn't want children back there while I was moving, no matter how slow I was going, which means keeping an eye on little ones even more.
That being said, I really like the look and size of the Swingback, and if we felt compelled to have one, I'd definitely get the stainless rail system around it. Expensive or not, I'd feel a lot better having that railing back there while underway.
On the other hand, we love our rear lounge on the SSLX, but I don't think it is available on very many models, which I think is a shame. It's very comfortable for two adults, and we feel safe if a child is back there...as long as an adult is sitting right there next to them! But then, we rarely have children on board, so it's a great place to watch the light play off the wake from the engine or to get sun and just relax. It surprises me that Bennington doesn't offer an upscaled version of this lounge on the G series. I think it's a great idea for retirees
We've said if we ever upgraded, it would be to either a 23 GSB with the Swingback, or the 23 GCW with the dual loungers. Someone correct me if I'm wrong but I believe the option called the Stainless Steel Railkeeper (Swingback) for $747 is the rail system surrounding the Swingback?
A swingback with the surrounding rail system. It doesn't look like much protection for little ones, though.