I have to hold my hands up and say that I was very, VERY skeptical about the advent of clip-on tuners. I primarily play electric or electro-acoustic guitars, so I'm used to plugging into handheld or pedal chromatic tuners as a matter of course, and I didn't think a clip-on could ever compete.
Consider me all turned around on the subject. In A/B testing against a Korg CA-2 plug-in tuner, the Bullet Tuner is just as accurate. In fact, it is if anything more "reassuring" than the Korg, which is sometimes a bit too sensitive to slight pitch changes in the decay of a string's vibration (meaning you might have to repeatedly pluck the string while under adjustment in order not to be driven to distraction by constant changes). The Bullet Tuner offers you a straight answer.
The biggest difference is sheer convenience. The Bullet Tuner clips on and stays out of my way when not in use, and is easily brought to life when needed. I have used it for quick tune ups during practice/recording, for string replacement, and for tone checks during action/intonation adjustments and other maintenance, and it does it all admirably – and with much less fuss than a traditional tuner. The swivel and pivot of the head is great for visibility and the metal casing feels reassuringly heavy and durable.
There are some minor niggles. The tuner is very sensitive to its position on the guitar's headstock (if playing an electric – it should be attached to the edge of the soundhole if playing an acoustic) and placed at the far end of a "fat Strat" headstock, it struggled to pick up the low E string. Pretty surprising, considering its manufacturer! It also would have been nice to have a rechargeable battery rather than the disposable cell battery used here (the tuner is small, but there's definitely room that could have been used to fit a USB port for charging).
All in all, though, this is a great piece of kit that should have you spending less time tuning and more time playing. Consider me a convert :-)