It seems that no-ip.org want people to register and pay for the service - certainly if you don't want to have to verify the account every 30 days.

Thankfully I only have 2 such accounts I need to verify, so I've opted to save my cash for the time being....

So long as you have custom provider available on ddns setup screen and a domain name you own to transfer into it you can use dns.he.net, free, no faf, no messing about. It's a bit of a tech user's system and they call it a beta but it has no real restrictions too. I got it, not originally for DDNS (but that's useful too) but, for being able to setup any sort of record I want, not just what the provider wants to sell me.