Daddario PW-CT-12 Micro Headstock Tuner

It's about the smallest clip tuner in existence, it's totally unobtrusive, you can stick it on the headstock and just leave it there forever. I'm using these on all my electric and acoustic guitars, also I've used it on my bass ukulele in the past.

The pros:
-small footprint
-quicker turn-on and turn-off time than the previous version, PW-CT-10
-quick response
- it's reasonably accurate for the practical purposes. My Korg CA-50 seems to be more precise.
- reliability. I've had two of the previous version for what, eight years now, and never had issues with them, if that's any indication.

The cons:
- tuning sensitivity. It sometimes struggles with the B string on a guitar, shows it as F#. And while it is possible to use this thing on a bass, you'd better use 12th fret harmonics to tune it. It doesn't pick the low B up on my five-string.
- viewing angles could be better. Sometimes the shape of the headstock prevents you from turning the screen directly at you, and it gets hard to see what's going on. The previous green version has better angles.
- it's a touch expensive for what it is.

Overall, it's a good, very small tuner. There are better options if the size isn't the primary concern.