From their web page:
"Q-Tuners are a revolutionary new approach to passive pickup design. They combine the hi fidelity punch of an active with a signal clarity unavailable anywhere else. Their resonance frequency appears further up the sound spectrum providing a 1:1 conversion of your performance to electrical signal. In fact they're so good, they faithfully reproduce the delicate harmonics between 5 and 10 kHz, a frequency range active electronics "filter" out and other passives don't even see."
The tone control they suggest should roll off highs before 5 kHz. Even if the tone controls on the guitar does not roll off the additional highs, most guitar amps roll of the high frequencies before this point as well, so any gain in harmonics in the 5 and 10 kHz range will not make out of you amp. It is also my experience the more sensitive a pick is, the more unforgiving the pickup is, and the harder it is to get a constant sound.