This can make a cheap tuner tuner pick up higher and lower notes, and as harpist it enables me to tune up in a noisy environment. I've used cheaper pickups and they are nowhere near as sensitive. The cable is really long, which is useful and the pickup is chunky.
Sadly the cable failed within months, the same thing happened to my old PE-2. As a big fan of Peterson tuners this is a shame. I am now looking at the Korg models which appear to have better cable support.
If you look after the cable carefully, this is great.
I bought this for one guitar I was touring with (as the guitar tech) which didn't have a pickup and was used onstage played into a microphone. This enabled me to tune the guitar easily and accurately off stage. I also used this into the Peterson Strobo iPhone app too which is great.