Without disclosing specific models Nemo uses a questionable analogy of the personalities of two different women and another using two different German automobiles to describe basic differences with four subwoofers, REL, Rythmik and SVS and JL Audio. He also places something on appearances.
Three of these subwoofers is equipped with differing methods of equalization, two add room optimization all are vital in producing variable presentations. With the exception of REL they all meet or exceed their claimed low frequency response.
Better to give Nemo his twenty thousand leagues under whatever and begin with mrteeves’ philosophical differences.
All REL’s are sub bass speakers. Rythmik has optional frequency cut and boost and JL Audio F series has an internal frequency generator and a calibrated microphone to automatically (only) adjust the frequency response. All are set-it and forget-it subs.
The SVS uses a smartphone (remote control) based application that allows you to see what your hearing while making crossover, phase, frequency, Q and volume adjustments to your liking. And the ability add those settings and two others to memory presets. If you want the SVS to sound like a REL it’s up to you.
Best of all you can change the volume by remote control as well as the presets all from the listening position. Velodyne offered far more detail version of this almost two decades ago in their DD and DD Plus lines.
mrteeves, "No right or wrong, it comes down to one preference." All the best with your search.