They're a real handy tuner - can be used in a noisy room, will lock on to about anything the clamp will fit - guitar, banjo, mandolin, fiddle, autoharp (with care), etc.

They run about $50 to $60 US, depending on who you know. There's a new "white" dumbed down edition (the originals are black) that doesn't have the backlight or ability to tune to non-standard pitch, and they cost about $30. I've got one of each, and I'd go for the more expensive - in a dark pub, or around a campfire that backlight is
a real saviour.

The downside to them is that the clamp and swivel mechanism is not the strongest in the world and you need to treat it with care or it will break.

I also discovered just the other day, on guitar, that on the low E string I couldn't get it to display when using a flat pick, but when I plucked with my thumb it came right up. Something to do with overtones or transients, or whatever ??