This unit arrived with 2 of the knobs pushed in flush with the casing, but I was able to remove cover and raise them back up.
The biggest quality issue I’ve found is that the POTS used are not linear, which really can make adjustment a little difficult.
As an example of this, you may turn the adjuster through 20% of its adjustment range, but have already hit 95%, and the remaining 5% of adjustment left is spread over the remaining travel of the POT switch. I can see where this would leave many to get the impression that the device doesn’t cover the entire range it should, but it does seem to hit the full range, just NOT with any linear progression.
I get 85% of available gain in the first 20% of adjuster knob travel, with almost no additional gain after that first 20%.

So does it work? Yes
Can it adjust the frequency ranges it advertises? Yes, but not with precision.
Is it "clean" as far as signal mod is related? yes, hasn’t added any measurable distortion to my system.
Internal grounding ok? No signal or ground loops detected, but that may depend on vehicle electronics as much as the unit.

Works good as a line driver, basic signal amp, and as a basic cross-over.
If you need/want precise control over your cross-over points, this is not the unit for you.
If you’re looking for something to boost signal strength on your RCA’s, this works fine.