I did the same for several years at my last job (although with Friday off so I had long weekends). It was great and I'd encourage anyone to try it if they can.

I definitely felt like it made me more productive per hour worked. A shorter week added a little bit of time pressure that helped me stay focused, and I'd often finish something in four days that might otherwise have stretched to five.

Total output was probably a little lower, but I took an equivalent pay cut when I reduced my hours.

I was only able to make that arrangement after I'd been at the job for a while. When I changed jobs, I went back to five days a week, and I'm definitely missing the long weekends.