I would thoroughly recommend the TU-3 to any guitarists in search of a tuner pedal. I have not been disappointed with it since buying it.
It is very easy to use, the bright display is easy to read, and it is very sensitive. I have struggled with clip-on tuners in the past, as I tend to play a lot in alternative tunings (such as DADGAD) in which tuning is critical however some tuners struggle to pick up the bottom string or just do not have the sensitivy to cope properly. However, the TU-3 has no such problems, and every time I use it my acoustic guitar sounds perfectly in tune. Yes it is a bit more expensive than some of the other tuner pedals around, but sometimes you get what you pay for. Boss is a good make, and this pedal has the added advantage of being able to power up to 7 other Boss pedals when combined with the relevant adaptor and cable.