Maybe it's just me but it seems as if a four day work week would almost have to come at the expense of a larger basket of time off that you can take when you want to. Which, in general, isn't a tradeoff I would like--nor, I imagine, would many people who prefer to take trips rather than having more free time around their home.
I get 5 weeks of PTO (25 days, or 200 hours) now*. If I worked 4x10 weeks, I'd expect the most fair equivalent amount of PTO would be 5 weeks (now 20 days, still 200 hours).
On one hand, that is fewer Mondays or Wednesdays that you could take off, but it seems a more than fair trade, given that you don't ever have to take a Friday off.
Indeed, if the employer said "now that we have 4 day weeks, we're taking away 10 days of PTO, leaving you with 15 (150 hours instead of 200)", I'd then view that as something taken away.
* It's possible that it's actually 24 days, not 25, and I'm too lazy to chase it down in the employee handbook. For this post, it's 25. :)
