I love the 9/80 schedule that my employer has. The off Friday is really useful to get all those business hour things done that normally you'd need to take time off for, like having a repairman come or doctor's visits. And one less commute per two weeks is also great. Officially, my employer oddly does not allow flex time so everyone is supposed to work the same set hours, but I have never seen this enforced at all.
The extra hour per day makes for a longer day (so you have to go in earlier or stay at work later), and if you have an unproductive day for some reason, more time is wasted. I see my kids a bit less in the evening because of this, which is one big downside.
Coming here, I was skeptical that the "off friday" would really be a day off, and if I'd be expected to regularly work that day. But it is treated as a day off, and most people do not work it. On a crunch effort, people might work it, but that's rare, not "mandatory", and usually paid overtime would be available for that. And even if paid OT isn't available and you want to work a Friday, unpaid overtime is credited against any absent/sick time you take off.
There are never any bugs you haven't found yet.