The Adjustable Force Fins are the only ones designed to fit over wading boots, hence the two adjustable straps over the top of each foot. All others are intended to be used with neoprene feet in stockingfoot waders (which, some of my friends say, is a much better experience than using the Adjustables with heavy wading boots.) Regardless, if you're thinking about a pair of non-Adjustables, I'd be damned sure they fit properly since if they don't, you risk having them coming off at an inopportune time and the don't float.
As a strategy, it might be worthwhile to bring your wading boots along to a fly shop and then seeing if they'll fit in any of the non-Adjustables. Buying a pair over the Internet without trying them on seems to me to be a sure-fire invitation to an unhappy experience if they don't fit properly (Force Fins don't float, so if an ill-fitting one comes loose at an inopportune time, you could be SOL). If the standard fins don't fit, then get ready for the sticker shock associated with Adjustable Force Fins. They're very efficient, very expensive, and very sought-after, so nobody is likely to offer even a well-used pair on the cheap.
Just sayin' . . .
K