It's a tuner guitar / bass classic, can be connected between the amp and guitar, just a guitar or use it in acoustics (but less accurate). It also has a feature where it emits notes but I've never served! it detects the string to tune automatically, but you can also do it manually, it is very easy to use.
It is compact, robust (it supports many falls!), It operates on two AAA batteries (small) that are still backgrounds for a year.
For € 22 it's a very good product and I will take probably the same.