@M0YNG Emphasise the decentralised aspects of mastodon as a whole. I think that will appeal to radio users.
I really like that I can follow people from all over the place, but then visit the "local" section to only see things posted by the ham community.
I also really appreciate the general level of friendliness I've seen on mastodon, I think it should appeal to anyone sick of the toxicity of the big sites.
@M0YNG and finally, if you're talking to an older group with less experience of social media this is probably a great starting point.