I have the HSU STF-2 and M22's. Awesome.
One of the main reasons I considered an HSU sub is because they are down firing. This means, someone can kick it and not go "Oops, I just bashed in your very expensive subwoofer, sorry." Then again, it is under my computer desk serving as a vibrating footrest. It serves its purpose well in that area too.
You shouldn't feel any need to upgrade your sub if you have a smaller room. If you get really excited, the EP500 would be the next upgrade. However, the HSU STF-2 is in my opinion the best budget subwoofer. The VTF-2 is actually the exact same subwoofer except it has two tuning modes. That's why it is $100 more. However, a subwoofer always usually wants to go the lowest, which is what the STF-2 is tuned for, so it is the best deal.
