I have the Monoprice subs in house, but haven't even unboxed them yet because I have been so busy with other things. There is going to be a delay on this review. I lost access to my usual test site and had to find a new one, and the kind of site I need is not easy to find in my area.
As for a comparison, I can only speculate at this point. My guess is that the Monoprice sub will be able to get louder and stay cleaner at deep frequencies. It looks like a bit more capable sub overall, but it is more expensive. The Hsu is a bit over 400 shipped, and the Monoprice is 500 not including shipping, but the shipping weight is 93 lbs so it won't be that cheap to ship. As for traditional bass music frequencies, 40 Hz and above, I think they will be about even for maximum output, but the Monoprice sub may be able to have lower distortion for the same output. Lower distorton at max output won't really be a factor if you don't push them to the limit though. I would say if you are interested in content with frequencies below 40 Hz, the Monoprice is the one to get. Keep in mind that the only music with content that low is some pipe organ music and some electronic music.
One nice thing about the Hsu for people who like to tinker with placement is it is pretty light at 42 lbs. The Monoprice is a bit more of a chore to move around at 72 lbs. That is a big help to reviewers who have to move these things around a lot, so that may skewer my perspective a bit!