Although I'm in Australia, I work for a UK-based edtech company (Wonde) that operates a four-day workweek -- having joined just over three months ago. I know that I can only contribute anecdata, but from my perspective I've not seen any reduction in output.
Indeed, I've seen fewer meetings, and meetings defaulting to thirty minutes, rather than sixty. I've also seen more async communication -- not once have I received the dreaded lonely "Hello" in Slack. It's of course not all sunshine and lollipops. People aren't always available, so you have to work around or wait. On a personal level, I find I approach each day with more energy and enthusiasm, and I love that I get to spend more time with my family and can (shock!) go out to lunch with my wife during the week while the kids are at school. There seems to be a direct correlation between my improved personal life and an improved professional life.
Indeed, I've seen fewer meetings, and meetings defaulting to thirty minutes, rather than sixty. I've also seen more async communication -- not once have I received the dreaded lonely "Hello" in Slack. It's of course not all sunshine and lollipops. People aren't always available, so you have to work around or wait. On a personal level, I find I approach each day with more energy and enthusiasm, and I love that I get to spend more time with my family and can (shock!) go out to lunch with my wife during the week while the kids are at school. There seems to be a direct correlation between my improved personal life and an improved professional life.