Nice review Gene. I agree with your assessment that RBH might want to be a little less aggressive with the limiter on this sub. The direct competition for this subwoofer seem to be the Hsu VTF-2 mk5 and the SVS PB 2000. If the RBH sub can eek out about 3 dB more without significantly increasing the distortion, then it is pretty comparable to the Hsu sub. While the Hsu sub is cheaper, the RBH looks much better. I would definitely spend the extra money on the RBH sub for the nicer looking finish, if the performance between the two are quite close. If the performance of the Hsu it a bit better in terms of raw output, then the extra cost of the RBH becomes a tougher sell. Also of note, the price of the RBH sub is very close to the SVS PB or PC 2000, which has a lot more output, that is clean. But, it doesn't have port tuning capabilities. I am only comparing these two subs to the RBH subwoofer, since they were recently reviewed and measured on Audioholics.
Yet another comparable subwoofer would be the Rythmik LVX12, that also has port tuning capabilities and is quite close to the price. The finish isn't as as nice as on the RBH, but I think it has more output and has servo technology in the sub. This leads me to believe that the Rythmik might just be a better sub in a least a couple of performance areas. The subwoofer market is a competitive market right now. This is excellent for us thinking about purchasing subwoofers, since each year the subs that we could get per dollar is getting better and better and sometimes there are even more budget friendly options like the RBH that also look great.