I've added MOST of the M-Carbo parts for the Sub2000 to mine, and have been really impressed with how well they work.
(Installing the spring kit was a challenge, but the M-Carbo video steps you right through the process. That simple little gun is quite complex inside (in a weird sort of way) e -- it's far different, internally than any gun I've owned, and nothing is as it seems or expected! Without that video I would have been LOST!! )
I've looked at a number of folding mounts, but decided on a Millett quick release mount (and I leave the optic, a SIG Romeo5 on it.) It just takes a minute or so (probably less if I'm in a hurry), and it does hold zero. The difference? The Millett mount -- here's a link -- and it's only $18.99 from Amazon Prime.
https://smile.amazon.com/gp/product/B00I00MP0U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 I've used mine a number of times, and it seems to hold true very well.
If you feel you MUST have a folding mount, the M-Carbo seems to be one of the best available -- and they're all expensive.
For an extra minute or two in getting ready each time I unfold my Sub2000 from my Laptop case -- the folded gun, and 5 mags fit nicely in the case -- I'll just not spend the extra $120.
My son, who is a AR enthusiast, has a SIG MPX with some extras installed. My M-Carbo-rized Sub2000 shoots right with it, and does it for about 1/3 the $$$. (We both use the Romeo5 system.)
