Well, I still haven't fully tried these out yet, since at our demo on Friday, I didn't want to be experimenting with new gear in front of an audience. But with the larger size gloves, I was able to fit leather gloves inside without any trouble.
From handling them a little, it looks like the clamshell can get caught on the crossguard, particularly when transitioning in and out of the "thumb grip" and rolling the sword in your hand. It looks like the best way to avoid this is to slide your hand back a little and hold it closer to the center of the grip than you're used to, by maybe an inch.