I had a bit of trouble running DTRegister after installing (I'm a new joomla user). I submitted a ticket and it was answered in UNDER ONE HOUR with what I needed to do. Which was to install the CURL library. After that it worked great.
Also, a feature I was interested in was added within days in the next release. I went to their forum and suggested it. It was a simple request/feature, but I was happy to see that it was added and taken care of so quickly.
DTRegister's support, whether through email or their forum, is top notch. Whatever questions or needs I have they are answered promptly and with instructions I can follow.
A good functional product at a great price, and fantastic support.