I've been watching youtube videos of a lot of technical dives lately and I've decided to put off cave/technical training for another year. Maybe when I get to 200 dives or something. However, I do have a question. Why do tech/cave divers not use full facemasks with comms? I've even looked specifically for these in videos, and found none. Is there some inherent incompatibility between the two? Certainly cost cannot be an issue given all the other extreme costs involved, so I'm curious what it is.