I've partially taped the vents closed when I'm getting to much air flow or my breath is fogging from the bottom because of a mask. It's as effective as it is cheap. I put the tape on the inside so you can't see it.I get cold pretty easily. For example I bought OR Alti Mitts on sale after a frigid day at Beaver Creek in January. Temp was about 9F, 15mph winds, snowing. My hands were frozen in the Arc'teryx Fission mitts I'd bought for the season, with knit poly liners. The OR mitts are ridiculous and I only plan to use them on cold days but that gives you an idea of where I am coming from.
The main thing is how much wind passes through the masks. My contacts will start to glaze over at high speeds with lots of cold air flow through the goggles. I am hoping the MFI mask blocks more wind from coming in the underside of the goggle, and read one comment comparing Wool MFI to the Tech Baclava, saying the midweight wool blocked more wind.