I have a rather large head and searched for years to find a mask that didn't leak. Several years ago I found the Mares Lirica and loved it (realize its not frameless but I'll get there in a moment).
I was on my third Lirica (purchased about 1 year ago) when I started a trimix class in December. During the course I became anowed with the Lirica because it seemed every time I got into a critical situation during drills the mask would collapse inward on my face and flood. I finally realized the strap on the latest Lirica I had was too short, it was adjust to the last ridge on the strap and still could have been a little looser. I replaced the strap with an old Cressi strap that was an older Lirica and that improved things but by then I had decided I needed another mask.
LDS in Hong Kong had the Scubapro Frameless and a Sherwood Mako, which was similar to the Oceanic Shadow. I picked up both mask and the Scubapro was much beefier and felt better made. I bought a Taiwanese knockoff of the Shadow 3 years ago and used it once and gave it away, now I never buy a copy or knockoff as I definitely believe you get what you pay for.
I bought the Scubapro and used it last week for the first time, did 6 dives over Easter without any problems and know I made the right choice.
Drew