I agree with nightflier, how you tune the sub is very much key to how it will ultimately sound. In most rooms, I feel that a parametric EQ is absolutely essential because standing waves at low frequencies are very common. This can create an excessively boomy sound with ANY subwoofer, and the parametric EQ is the most cost effective way to control them. Once you get the actual in-room frequency characteristics of the sub as close to flat as possible, then it's that much easier to integrate it with the mains. That's why I think that the general characteristics of the subwoofer's design are only part of what you need to consider. It doesn't matter how well a sub is designed, or what type of cabinet it has, if the room acoustics are a problem. And with most small or medium sized rooms, the room acoustics will pose a problem for the low frequencies, and make ANY subwoofer not perform at its best.

Adire has an excellent reputation among DIY hobbyists, and in actuality, their main market remains just selling drivers and other parts for making your own subwoofers (they also do contract design work for other companies). They've made several different subwoofer designs (you can look at some of them in downloadable papers), but market very few finished subwoofers. I believe that their Washington facility only has 15 employees, and the finished subwoofers and speakers are the only things that they actually assemble there. The Rava is the only preassembled model that they keep in inventory, all of the other speakers that they market are built to order, and even with the Rava you can specify modifications if you have a certain type of specification that you're looking for. Their drivers and other components are made by contract manufacturers (their drivers are U.S. made BTW).

I wouldn't let the low price sway you, the Rava is worth considering. Your room is a bit large, but the Shiva driver that's on the Rava moves a LOT of air, so it very well might be enough. You're really the primary judge of how much bass you really need (in my smaller room, I know that two Ravas would be overkill). The in-room response on a Rava (in my room after equalization) is pretty much flat all the way down to 25 Hz with decent output down to 20 Hz. Subjectively, it's pretty tight and really shines with acoustic music, but still has excellent depth for HT sources.

But, I don't have enough exposure to more expensive subs to tell you how the Rava would directly compare. Still though, I firmly believe that no matter what subwoofer you go with, a properly tuned Rava can and will outperform much more expensive models that have not been properly setup and equalized.