I don't think that is a particularly small room; while it is not tall and is quite narrow, the length provides quite a few cubic feet, no? You still have to push all that air around a bit.
I had similar concerns with child and pet interaction, so decided early on that I wanted a down-firing sub (ended up with the SVS PB12-ISD, with which I am thrilled). So, you would be safe and solid with the Hsu.
I have immense respect and admiration for those people who are successfully building their own subs; I know that I lack the patience to learn everything necessary to build something comparable in performance to what SVS and Hsu already produce. Likewise, my understanding is that not every DIY driver is equally suitable for down-firing application.
