I had their old Level II sub, I thought it sounded better than the popular Sony sawm 40. Sounded pretty tight compared to the Sony. however it is pretty much dead below 28 Hz. Returned it because I decided to build an SVS clone instead. HTD has a great return policy, I would just buy it and demo it for awhile. They will pay for the return shipping so you will be out nothing unless they changed their return policy. I have their Level II speakers and they sound great!
Here is a link to an ealier thread on the levell II sub, After I built my sub the LII sub is definately missing