Four other folks at our company work 4x10, including the CEO, and it works just fine. Friday is fucking sacrosanct: no emails, no phone calls, no contact of any kind. If a fire flares up, other people in the office deal with it.
And when I say 4x10, I mean it. We track our time pretty religiously, and our most bust-ass employee has averaged about 42 hours a week over 18 months.
And yes, we're a tech company