idk, the F20 felt great when I first put them on, but I've been riding them for about 20 days now and they still aren't really breaking in. That might seem like a good thing as far as longevity, but, on those first to last chair days, the f20 kinda feel like wearing a stiff shell with no liner...especially if wearing a lighter/performance sock.
At first, the worst thing was getting painful rubbing on my Achilles tendon (switching to superfeet insoles minimized that by about 75%), but I'm still getting other sore areas due to the thin, spotty "fusion liner". I really don't wanna go the super thick sock route, but that may be the only way to get F20s close that full liner comfort.
I'm gonna keep wearing mine because they're now (barely) acceptably comfortable, but, in hindsight, I would skip the F-series and get a standard boot with a full removable liner (or maybe try burton shrinkage)
This is discouraging, even though feet are like fingerprints. I think I will buy my boots early (next month) and wear them everyday, on the carpet, around the house just to see if problems arise, before my LBS return policy expires. It's either that or get stuck with miserable feet on the hill all day.