It's been 2 years since I use it to be able to provide troubleshoots anywhere and anytime without having my PolyTune Mini or even an electrical outlet handy.
I had various korgs before that worked on the same principle.
It is not very precise and has trouble sometimes with serious If a 5 string, but somehow when you are in a situation where you need a quality impeccable tuning (studio, live ...) was something else to give.
It really serve to give the house when you want just a little scratch without turning all his gear or when one takes acoustic drill, etc ...
He is there to help when you can not have a tuner pro and that we care.
Short, less than 5 euros I am very happy and if it breaks I bought 5 for a stock in advance!