Duck DNS includes step by step instructions on how to set up their service on a wide variety of operating systems. There even are instruction on how to set it up on raspberry pi, mikrotik routers, tomatoUSB as well as multiple ways for Linux, Windows and OSX.
Routers and NVRs that give you set options (that don't include Duck DNS) won't work with Duck DNS. Apparently Duck DNS claims they support DynDNS or something of the sort, but the information it gives you, there's nowhere to plug it in in these boxes.
Dynu provides thorough setup instructions on different routers and operating systems. Everything is explained in a detailed and understandable way even for beginners.
If your domain name uses their nameservers, you can set up other nameserver records for your sub-domain names if you want to use those sub-domain names with other hosting providers. This kind of flexibility does not exist anywhere else.
You do get to use all features of Dynu services with a free account. But if you need to use say 300 hostnames, you may need to pay $9.99/year membership fee. Usually, a free account is more than enough.
Seems to be only for customers who have purchased other products, not freely available to the public? Unclear how to register or use a domain/subdomain name from Hurricane Electric.
Being a joint effort with APNIC and CloudFlare, 1.1.1.1 aims to be more privacy-focused. They have taken a lot of steps to ensure none of your data will be in their Anycast servers.
Because of the nature of 1.1.1.1 not being reserved - some routers use this IP address space to serve their admin web consoles. However, some manufacturers have been notified and are deploying updates.