I stick with ten rounders. Executing a reload while changing positions on a prop takes no time at all, and certainly doesn’t influence my results at all.
I have seen a lot of these mag extensions be a bit finicky function wise, and some matches will state in the COF description that a reload must be done so that mitigates the extra capacity stuff.
To me, the whole point of a stage requiring more than ten rounds is to force the reload, and add a technique that must be mastered to the stage/ match, so I think any of these stages should require a reload, and not have people looking for an end around