Sure never heard of them referred to as a "gimmick" Of course they work on handguns & lots of people use them. I've sold hundreds of them in both sizes. I would say that the Express sight can be a bit faster but you can't focus on it as easy as you can with a peep and there's your "fact", at least not with older eyes & that's what we're talking about here.
I use to make some Express sights but they didn't sell well at all.

Dick