Out of 5 full face masks, the F40 is the best one yet for me. The F40 is the most comfortable, lightest, best fitting, easiest to put on, and best sealing out of the 5. It is like a much improved Evora full face, another hybrid.
It is very nice to have a mask not covering the top of my nose where a sore was beginning to form from an F20.
The straps do not need to be as tight as F10/F20 to get the F40 to seal. My pressure goes to 20cm. The headgear was easily adjusted and not nearly as irritating as the Evora FF and regular full-face masks. The magnetic strap connectors are easier to use than any connection type so far.
My F10s and F20s were Large sizes. I am using standard headgear and medium-size mask F40 which seems to fit better than the large F10/F20s.
My AHIs have not improved, but I am feeling more rested than usual maybe due to the minimalist size of the mask and headgear not being so irritating. I roll around a bunch during sleep. The F40 makes that easier.