The lighter-style, double-folding deployant is quite new, so far fewer people have experience with them.
Re longevity: I think both deployants will last longer than you or I will, and straps will last just as long with either of them (and far longer with either of these deployants than straps would last with a tang buckle).
Re attaching the double-folding deployant to the strap: See photo below. This deployant uses a fixed bar and small detent screw instead of a springbar to attach the buckle to the strap.
Re strap length: I'd strongly suggest that you first get the buckle and then figure out strap length. I can't easily measure either buckle right now, but I can tell you that for a 38.5mm Lange, when used with the older, heavier, single-fold deployant, I use a strap measuring 45mm x 110mm to fit my 6" wrist. Yes, 45mm is quite short, but as you can see from the photo below, the buckle (not the buckle head, but the curve of the buckle shank) is centered underneath my wrist using those measurements. With the newer, lighter, double-fold deployant, I could probably use a standard Lange short strap or maybe even a regular-length Lange strap (though I haven't actually used that buckle on a watch).
Personally, I think the older, heavier, single-fold deployants look more "Lange-like" because they're beefier and, as Dean said, more balanced with most Lange models. I could see using the double-folding deployant on a lighter watch such as a Saxonia 35mm, a Saxonia Thin, or maybe an 1815 or a Cabaret. The big advantage of the double-folding deployant is that you probably won't need a custom strap, and it also might be slightly more comfortable on your small wrist (though I find the single-folding deployants to be fine as long as the strap length property centers the buckle on my wrist).
Also, you may find the comments that people wrote in
this old thread to be helpful.
This message has been edited by CR on 2016-04-25 13:12:36