To the OP:
I actually have both the QB8 MK III (20A) and a Niagara 5000 (and a Shunyata Denali X) in different systems. I’ve directly compared the Nordost QB8 and Niagara units in one of my systems - and in the dealer’s showroom. As noted by others - they are different products. Both are distributors in function but the AQ adds conditioning. If you have clean power, they sound fairly similar - the AQ a bit darker in background and the Nordost felt a bit more dynamic and lighter on its feet. (I clearly lack the language of a reviewer). If you have “iffy” power quality - AQ hands down. If you have clean power and are less worried about lightning strikes etc, then I like the Nordost a bit better. Note - I also auditioned the Nordost QB 10 Reference unit and passed as it didn’t bring enough more to the table for the price. It was good, but not $18k good - to me.
In my view, the new Shunyata X products are a bit of a step up from either.
One last note: I run my QB 8 with Nordost Valhalla 2 cables. I did not audition the AQ with similarly high quality power cords and it’s entirely possible I would have come to a different conclusion on it relative merits had I tried AQ Dragon cables with it.
As always: YMMV.
Best,

