You have to lift the lever extra high to get it started past the very end of the slot.
No, QD sling mounts will not fit the hole that is provided as shipped.
I asked this question on March 14th and it was only approved by OP on July 15th (5 months to just approve a question in unacceptable). Meanwhile I purchased it, so now I'll answer my own question. It does NOT come with the QD cups. Looks like it might, but the holes are for installing third party QD cups. I ended up purchasing the threaded ones by Grovtec (GTHM289) cups for less than ten bucks. That required tapping the existing holes, which wasn't difficult to do in the polymer. Put a little JB Quick on them and they're there forever and look OEM. As one reviewer stated, the slots are not large enough for even a 1 inch sling. Other than these shortcomings, I like the stock for the money. I wanted a minimalist style, with QD cups.
Pull down on the lever that allows the stock to collapse. Then slide the stock off the buffer tube.
I had to use three or four strips of electrical tape to get it right.
You can remove the XTS AR Collapsible Skeleton Stock the same way you remove standard AR stock. You will pull down on the adjustment lever and slide the stock off the buffer tube.