The MG-1 is a cool twist on headstock tuners.
It's a sweet little tuner that uses a magnet to attach the tuner one of the machine heads. It's transducer is able to pick up the tuning for all of the strings without having to move it from one machine head to the next. It uses readily available CR2032 batteries (which we also stock) which should last about 30 hours.
The Korg Magnetune is a chromatic tuner so it will work for any instruments that have a metal tuning post to attach to.
Check out the korg website at http://www.korg.com/us/products/tuners/magnetune/ for more information.