Overstuffed wide seats frequently don't work well for typical bicycle riding because they tend to interfere with pedaling. This is why they get bad reviews by normal bicycle reviewers.
On a gas-engined motorized bike however, most of the time you probably aren't pedaling at all. This means that perfect leg extension isn't needed, so you can lower the seat 3-4 inches below where you'd have it on a non-motorized bike, and the seat will be a lot more comfortable to sit on. If you get a quick-release seat post this adjustment is easy to do, and it's easy to change if your engine should quit and you have to pedal back home.
--------
I put a cheap ($60) motorcycle bobber seat on mine, but it's not that much better overall than a bicycle seat really. The motorcycle seat pan is a bit larger and totally flat, which makes it somewhat more comfortable when not pedaling--but I can tell it's going to HURT if I ever have to pedal that thing 20 or 30 miles home.
~