DynDNS.org MailHop service?

Has anyone here used the dyndns.org mailhop service? Basically you would
run your mail server on a non-standard port and dyndns.org would relay
your mail to that port.

http://www.dyndns.org/services/mailhop/relay.html
http://www.dyndns.org/services/mailhop/faq.html

Has anyone had any problems/complaints with their service?
Thanks,
~M