Thanks for mentioning ConvertKit! We're happily building our niche product for creators and growing quickly.
Just a couple corrections, at the end of 2019 we were just under $20M ARR (Not $24M). Today we are at $22M ARR and 30,000 customers.
You can see all our numbers (updated in realtime) here on Baremetrics: http://convertkit.baremetrics.com
I'm happy to answer any questions.