There are a couple of types of tuners, considering "how the sound enters them":
- Those you connect your instrument to with a cable.
- Those that "hear" the instrument through a microphone.
- Those that pick up the sound via the instrument body, known as clip-on tuners.
Among the tuners mentioned above, there are those that listen to one note at a time and the slightly more expensive ones that can handle several notes simultaneously.
Then there are two different types, depending on how they tune:
- There are those that are only chromatic. This means it always shows which note is being played, regardless of the instrument.
- The other type has special programs for guitar, bass, violin, ukulele, etc. These tuners often also have a chromatic program.
Which of these you prefer is a matter of taste. Chromatic tuners may require slightly more prior knowledge. Here you need to know which string should be tuned to which note. In return, you can tune all your instruments, including those with special tunings, with one and the same device.
Those with special programs can figure out which string you are tuning and thus make it easier for inexperienced/comfortable users. But they work poorly when the strings are far too out of tune, for example after a string change. It's also very easy to accidentally use programs for the wrong instrument when tuning. It's not always that all the programs you need are available. D-tuned ukulele is not on all of them. Alternative tunings, for guitar for example, usually don't work.
My advice is to use the chromatic mode. Or a "chromatic only" tuner.
