We switched to Sendy too, because MailChimp's pricing leaves a lot to be desired. We have a list of about 10k subscribers, and we only send a campaign every 2-3 months. I have no idea why this is priced way higher than someone with 1k subscribers would sends 4 campaigns a month.
Sendy has worked perfectly for us. The UI could do with a lot of love, but its functionally fine.