Best tips I've heard on how #Mastodon can welcome people migrating from other social network. Summarizing:
– Don't say "about time".
– Avoid "well you're here now, so welcome."
– Best: don't mention any other social network at all.
Welcome them. Answer questions. Be helpful. Mentioning where they're coming from, even in passing can seem unintentionally smug. Sure let them vent if they initiate but don't turn Mastodon into the place where we focus more on where we were vs where we are now.