Facts: I imported a dozen blogs with a couple thousand entries and all manner of media embeds. Only took a few clicks and 20 mins; everything worked. I've also emailed with questions about plans, and received prompt personal and fully informative replies.
I had tried WP, Tumblr, and had started to fool with Jekyll when my posthaven invite came through. If you have better things to do with your time than fiddle with blog hosting, this migration is the way to go.
// Tip: Don't pre configure any blogs, just run the import which sets them up for you.