I think Bad Habits summed it up well. I would've gotten a cap if mine were a DC because of the pros he mentioned above. Mine is CM, so sleeping in it was out of question, unless I leave the gate open. Then why not just pitch a tent. So for small CM bed, a cap would not be as useful.
For marginal increase in utility, I was not willing to sacrifice the sliding rear window in my CM, one of the coolest features of CM.
I went with BAKFlip to be most flexible. When the item to be carried is large, then I could just flip one, two, or all of the panels open. The only time that my cover won't work is when I have to carry something large that needs to be dry. In that case, I will have to use some sort of vinyl cover to keep it dry. That, I figured, would be an easier solution than the solution required for the situation a cap could run into, having to carry something larger than a cap, dry or wet.