executive summary: i really like the ergonomics of the duostock. but the constuction sucks and it still suffers from all the weak points of the std collapsable stock.
first, the ergonomics are great. it fits perfectly in the pocket of my shoulder when extended to the second position. it is the most comfortable stock i have every used. i wish i could modify all my stocks like this. it is extremely fast to mount and once it is mounted, there is a lot of checkered butt plate surface area to grip the shoulder.
the only criticism of the ergonomics is that it is that the butt is a little wide. i would shave maybe 1/4 inch from it. other than that, the angle is perfect.
now, the downsides: the fit was very poor. when i called to order, i specifically asked when kind of stock tube to buy. the person at duostock said the universal model should fit any std collapsable stock tube (other that colt), but duostock molds are build on bushmaster stock tubes. so, i bought a bushmaster stock tube. however, when i tried to install it, the fit was extremely tight. so tight in fact, i could not even force the stock down to the first position. installation instructions did have a solution to this problem. duostock suggest sanding down the interior of the duostock. well i did. and, after a bunch of trial and error fittings, i finally got the stock to work well. now, it is fairly easy to move the stock btwn the different stock positions. but really, any new part that requires you to sand it down to work properly is not the best designed piece of equipment. this aspect really did not impress me.
in addition, the stock also suffers from the usu collapsable stock problems. the duostock is not that solid. there is a lot of rattle. while this does not affect the actual used of the rifle, i would like this stock to improve on the original design some more.
the rigidity of the stock also affect malfunction drills. when you get a stuck bolt malfunction in an ar, the proper procedure to clear it is to bang the gun down on the ground butt down while forcing the bolt down. collapsable stocks do not hold up to this treatment. they either break or collapse all the way, possibly injuring fingers.
cheek weld is another problem that was not solved. while i don't seem to have a problem w/ it b/c of my body shape. i can see some people having their cheek fall right inbtwn the stock and the buffer tube. moustaches beware.
the reason why i want to go to the next gen magpul is tha it solves all these problems. plus it has preset stock positions so you don't have to fumble w/ the stock to find 'your' personal position. oh, plus, it's supposed to be the best and it looks really cool.
so in conclusion, the duostock is not perfect, but it is definatly worth checking out, esp if you are on a budget.
oh and check out the duostock web site:
http://www.duostock.com/
it's sooooo cheesy!
here a close-up of the duostock