Their little 23mm unit seems to be the one I see everyone using; a one-piece outer hex/nipple back body with the window crimped in. Basically it seems everyone has their own flavor, but all basically the same design.
Though I have seen some, I think they were 32 Degrees, that had a wide-sweep dial, where the needle covered more like 220 or 260 degrees of the dial face, rather than the 90 degrees or so the more common ones do.
But that's fine, I just have a cool idea I want to look into. Thanks for the links!