I always revert to this small, UK-based PR agency who did it (with a few caveats due to PR being a 24/7 industry anyway...): https://www.radioactivepr.com/agency-impact-1-year-4-day-pay...

It is possible for small businesses to adopt it, but perhaps only really in the knowledge worker/high customer contact space. If you're a small ecommerce shop selling lots of actual stuff, then you'll definitely need to have greater role coverage than you otherwise might.