Having taken a few years off playing guitar due to illness, it's come as suprise to me how far some pieces of equipment have moved on. We have DI boxes that actually sound good, we have tiny all valve practice amps and we have super advanced (and sometimes bizarre) tuners. The Snark is an excellent example of the latter - a small, weird looking tuner that you simply clamp onto you guitar (or other instrument) to tune via vibration.
Despite some fiddle getting the battery seated (read the manual, you actually have to place the battery in the mounting not just jam it in the slot) and being skeptical of how well the Snark would work, I have to say I'm impressed. The display is beautifully clear, the tuning accurate (it even senses 12th fret harmonics) and it's easily small enough to have kicking around in your guitar case. To top it off, it costs virtually nothing.
I can't vouch for battery life and it's not the sturdiest piece of kit ever made so I'm not sure I would use it as my only tuner in a live environment. It will make a brilliant backup to a posh tuner pedal though and for home/studio/rehearsal use I don't think it can be faulted. Do yourself a favour and buy one, if not several!