That's where you need something like a MiniDSP and a mic to perform sub integration as it is a science. Simply plopping down any sub into your room and judging out of the box performance is no accurate way of assessing the true performance it could have. Even a small difference in timing can turn a sub from a hero into a zero. As someone who does this, I have to say most (sealed) subs end up sounding identical if corrected to the same curve.That excactly reflects my experiences with 3rd party sub integration vs. matching sub integration!
Which is why a company like REL exists in the hi-fi space. They make overpriced and under powered small subs that produce very little bass which people take as sounding "fast" and sounding more "seamless" to the speakers. When in reality you are just getting less bass and less extension down low.
These studio subwoofers follow a very similar idea. They also have fancy connections on the back but even that is completely useless if you have something like a MiniDSP, which every speaker+subwoofer system should have to begin with. And any onboard DSP and correction found on the sub is useless as well.
The Neuman KH750 at $1650 for a 10" sub to me is a robbery. A Rythmik F18 is $1750, an 18" sub that will eat it alive in every conceivable way and it won't even be close.
What really doesn't make sense is higher end studio monitors get VERY LOUD. 120+dB is the norm. But then they make these subs that are the complete opposite, where the mid-bass might get up to 105dB but with any real bass down low, you'll be lucky to get mid 90's.
Given a target curve should emphasize the lower frequencies over the midrange and treble, this problem of headroom gets even worse.
Sorry for the rant, I just hate to see people getting swindled by these companies. I really would like to see a massive change in the subwoofer space. You have the few dedicated sub companies that make great valued products, plus the DIY space which produces an even better value, and then you have everyone else who puts out these small underpowered subs and charge 2-5x more for it. And given it is beneficial to have dual or even more subs, this question of value gets to be much much worse.