Hello all,
The email list has worked well for me, and can be read by a neutral email app on my phone (K9Droid is what I use).
If we moved to Slack, I'd probably not participate. I find the stream-of-consciousness level of communication distracting enough using Microsoft Teams at work. My hobby interests rarely require instantaneous responses to someone else's thoughts.
I would caution against groups.io on political neutrality grounds. If you look at the page https://groups.io/static/pricing and search for "Indivisible", it is clear that those who run groups.io have a political axe to grind.
This is the reason that I dropped off of another email list (NTMS) when they moved to groups.io from Yahoo Groups.
Anyway, I prefer a simple email of plain text to something with flashy colors and obnoxious fonts. If something needs to be said graphically, include a URL to one of the many free hosting sites with the desired content.
My $0.02,
--- Zach N0ZGO