Funny you should mention the Ace Skeleton stock. Those are my favorite AR stocks and on the odd occasion when I contemplate installing an AR type stock on my 870, I always envision it with an Ace Skeleton stock.
I don't like collapsible stocks. Its not the fear that they will collapse when I don't want them to, it's more that they just feel funny... they feel "loose" and not "tight".
It might help you to know what length of pull (LOP) feels best for you and then choose the Ace stock that gives you that LOP when the mesa tactical adapapter and everything else is in place. The Ace products have several butt plates/pads of varying thickness so between the two sizes of stocks and the several pad thicknesses, you should be able to get the right LOP.
I would love to see a picture of you shotgun with the Mesa Tactical and Ace Skeleton stock installed!