I have an older Velodyne 15" servo sub that has been in HT duty since about 2000. It still works, but the volume control needs attention. The volume jumps strangely with small movements and is hard to set right. If anyone knows what might need to be done, it's probably worth fixing. I believe it uses the older class A/B amp.
When I recently shopped for subs for my listening room it was clear Velodyne no longer competed with many of the typical companies that now make the short list. I went with the Rythmik 12G servo subs and am thrilled. For pure HT, a ported model from many choices is no doubt a better decision today.