The ability to connect to the domain registrar through the API. This allows us to easily transfer domains between registrars, manage WHOIS records, and manage DNS records. They have an excellent support team. Not a lot, but I've never had a problem solving it. If you are looking for an easy to use API, this is the one! We are using it to automate the transfer of domains from one registrar to another. We're also using it to register domains. The best part I like most in this service is that it's free! It also has very clear instructions. You don't even have to be tech savvy to use it. There aren't any downsides really. If you're looking for something simple that doesn't cost anything then give them a try! I'm solving all my DNS needs with DNSimple so there isn't much more that we could ask for as far as features go.