Shadow E-Tuner: how/why doesn't it effect the guitar circuit

[Kindly Killer]

I just got one of these in the mail - I'm excited to try it, as it is the penultimate step in my quest to boil down my whole professional, catch-all rig to what I can fit in one guitar case and a small combo amp.

I'm puzzled by one thing: according to the manufacturers instructions, the input for the tuner is supposed to connect directly to the pickup lead; how can that be be neutral/of no effect? Or is it?

BTW I am going to put the tuner on a push/pull switch that mutes the output of the guitar. Since I'd have to roll the volume off to tune, anyway, I figure it's the same amount of manipulation. Just curious how the device could really have no effect.

[CRU JONES]

The tuner probably has a High input impedance. Likely it is a FET input op-amp buffer to the tuner. I think you should not have to worry about it effecting your tone.