It is simple, and the site is clean to a fault. There is zero advertising or service upselling - each page contains what it needs to and nothing else.
They're not the place to go to get cute with your TLDs, but for the standard TLDs, I refuse to go anywhere else. Even well-liked registrars like NameCheap are a big pile of spam in comparison.
That being said, I'd pay a lot more than that just for their clean (although slightly dated looking) interface. I'll be switching the rest of my domains to them in another month or so.
what ever happen to paying for things
I guess most people using their registrar service also use them as a host, so it makes sense to pay for it in the same way.
When you use NFSN for domain registration, you will probably also pay for whois privacy ($3.65/year) and DNS services. DNS services for domains registered with NFSN are $1.22/year, but if you host the website for that domain at NFSN you will only pay $0.41/year. So they do actually earn money on domain-only customers and they also give you an incentive to use them not just for domain registration.
/notanemployee