I like how easy it was to create templates, use them in other emails or even send from my phone! It's also very customizable which makes creating new ones super quick as well!! The customer service could be better because sometimes they don't respond quickly enough when you need help with something specific (like adding more fields).
Also not sure if this has been addressed but we are looking into having our own domain so maybe there will eventually come some kind customization options? We have used many different text editors over time including Wordpress plugins / free sites etc., none really gave us what exactly needed at first glance - until now :).