We have never used D-Link support services for our ethernet switches. We only looked for new firmware from their website, which was available for most of the models that are being used in our environment. Other than that, the official blogs and community pages of D-Link support were very helpful for small issues related to different features like NTP, stp, etc.
All the data we have needed is available on the Internet. We can also get help from blogs, as well as a D-Link partner available in our country, which provides support. We can submit issues to partners who provide support accordingly online or offline. We are satisfied with the support side of D-Link Ethernet Switches.
I have given it 9 out of 10 just because of its low cost and additional features that have been an integral part of any product, otherwise, the load management part was far more inferior as compared to the Cisco switches, as those switches have a spanning tree protocol built-in.