Just signed up and been testing your service. Overall: it's excellent!
I prefer your server based approach over listing aliases in DNS TXT records. It's a slightly disconcerting feeling to list a private/personal email address somewhere anyone can see it.
I also like how the "from" field is correctly populated with the senders address, this hasn't been done neatly on previous services I tried.
Obviously I can't comment on deliverability, reliability and so on, but can't really fault the experience so far.