I recently started running these for two cohorts of staff in my department, managers (middle and frontline) and administrative support. They're gaining traction.
The way I have structured them thus far is to identify a relevant topic each month based on anecdotal data from cohort members, leadership team members, and my own research/observations. I lightly design each session so there are a series of guiding questions to prompt discussion to help the group get more comfortable with each other. As a facilitator, I'll let the group deviate based on their interests.
My success metrics so far are very basic: overall attendance, repeat attendance, Level 1 reactionary survey feedback. Eventually I'll expand those metrics to something more tangible (and meaningful).