Garrett, it never occured to me that you'd been referring as much to the equipment's utility as the exercise's utility. My apologies, and thanks for clearing up my confusion.
Although I think you can do glute-ham raises without the bench. Lucky for me I train at a gym where they have an EliteFTS GHR. They have also rigged up a bench to allow for floor GHRs. Even so I used to train at a gym with no such equipment - we'd do partner GHRs on the floor. So I think of the GHR apparatus as a way to do GHRs better, not do them in the first place.
My exercise selection criteria these days are "doesn't aggravate my injuries when I do it" followed by "gives me a positive, transferable training effect." Otherwise, it's all good. I do prefer exercises where I'm standing up or hanging from things, but I'm willing to entertain anything that works. GHRs work for me, leg extensions don't - the first makes me stronger in other exercises, the second makes me hurt and doesn't make me stronger in anything else. From everything I've read here and in Cressey's article about leg extensions, I'm not surprised at either result.