I now have a Nordost QB8.
I have had the following power strip/conditioners ; PS Audio Dectet, BPT Strip, Blue Circle Audio, Isol-8, Weizhi PR6, MIT 6-Pole Outlet Filters and Mark Grant Audio. And DC blockers from Isotek.
All of them are reasonably priced, and most are parallel filters (or light series filters), none were regenerators or conditioners are such.
It’s hard to give an apples to apples comparison, because my system has changed over the years and also the power cables changed. All these products were good and improved things. But the Nordost beat them all. I did not want to believe it. It’s nothing but an aluminium box with nothing inside except a circuit board (that lifts the ground to the main outlet for preamp).
All the others, even those with purely parallel filtering, seemed to sit on the dynamics of the system compared to the Nordost.
Note this experience with the QB-8 is when I had Nordost Heimdall 2 power cables. Perhaps there is a special synergy with their own cables, and there is not such a gain when using other power cables.
One other feature of the QB4/8 is the grounding post and synergy with the Nordost QKore 1 grounding product. If you have a QB8 make sure the QKore 1 is your next upgrade, its that good.
I am a videophile as well as audiophile and the same experience desribed above applies on the visual side. Although the Blue Circle Audio gear was doing something quite distinct with the video filtering. I never got to try Blue Circle's higher end stuff and its a shame that company has now shut down.