HTML emails in general are full of contradictions. I plan to use the templates myself and I'm really excited about them. To answer your question though, it's just important to realize that much of these techniques won't work in the majority of email clients. iOS and some Android built-in email clients are the ones that this will be great for. But at the same time you still have to inline the vast majority of your CSS to get a consistent result in webmail clients.

In the end you have to know your audience. At my job, we have a lot of corporate types who are checking their emails in Outlook and also webmail so the emails I create have only two style rules in the head of the document with the rest inlined. Email is just really fragile and I personally believe you have to resign yourself to the fact that your email will break for some of your readers. When I create a website I expect it to work beautifully for over 95% of people. With email, I expect it to work 3/4 of the time. Maybe more if I'm lucky. That of course depends on the complexity of the email's design of course.