What are some alternatives?
When comparing zzzz.io and nsupdate.info, you can also consider the following products
FreeDNS - Free DNS hosting, lets you fully manage your own domain. Dynamic DNS and Static DNS services available. You may also create hosts off other domains that we host upon the domain owners consent, we have several domains to choose from!
Dyn - Managed DNS, Outsourced DNS & Anycast DNS
Duck DNS - Free dynamic DNS hosted on Amazon VPC
Dynu Dynamic DNS - Free dynamic DNS service with powerful features
No-IP - Dynamic DNS and Managed DNS Provider
ClouDNS.net - Free DNS, Cloud DNS, Managed DNS, GeoDNS and DDoS Protected DNS hosting with included web redirects, mail forwards and Round-Robin load balancing. Instant updates in Europe, North and South America, Asia and Australia.