I love the audiocontrol loc's. FWIW, the little 20-40 dollar pac ones are good too. They don't give a very high voltage, usually 1-2, but will give a clean signal and have summing capability. They'll take a much higher input voltage than the cheapo's too. Some of the audiocontrol's or higher end pac pro's will get up near 8v output and accept like 100w inputs. Long as you can get a flat signal out of the factory setup, that's just as good or better than an aftermarket.
The axxess and scosche ones have been junk. Like you said, most show a dirty signal even with the pots all the way down and the radio volume just strong enough to get a reading.