Everything is about positioning and dialing in the sub , you can buy very expensive one put it in the wrong spot and it would do more harm than a cheap one in slightly better position ,I would avoid all other subs TBH.
My first attempt was with fairly expensive REL , I spent hours trying to dial it in and re-positioning trusting just my ears , didn't work I've sold it in the end .
Second time I bought calibrated mic , done lots of measurements , spent lots of time moving sub from one place to another, I use SVS sub- built in eq filters help a lot as I can almost flatten annoying room mod with few dB reinforcement around mod frequency - final result sub is still with me and I can easily tell when I forget to turn it on . Build in EQ filters are quite handy as I was able to make few slightly different filters and compare while listening changing EQ from my mobile from listening position .
One thing I learnt , running LF "flat" down to the bottom is not my cup of tea , gentle slope down from 50Hz is much more pleasant to my ear but FR is just one of few things to consider .