That phrase, "for as long as you host with them", seems like the catch. So the domain won't be yours to take with you when you leave, then? Then what ultimate good will it do you, if their service turns out to not meet your needs? You will lose the domain, have to update your email addresses, have to contact everyone you know and tell them, you'll lose the traffic and possibly brand recognition...if it's free, it might not be worth the risk.