From the sound of it, I'm guessing they're similar, but I haven't had a chance to use Mandrill's templates. This started as an internal API we created and just decided to open up.

Our templates use a Django-like syntax, which let's you use loops and conditions in a easy to use way. Mandrill's might be the same or better. We done a lot with Django so that feels comfortable.

We're trying to focus on the experience of creating a new transactional or triggered email, so it's easy to go from "I have an idea for an email" to "I'm actually sending it." We use this internally with a simple Python script to send formatted summary emails of product usage each night and it's easy to set up -- write the script to fetch the data, create the email template and you're done.