I've always used clip on tuners on my guitars and basses. I never understood why you'd want to sacrifice prime real estate on your pedal board for a tuner. The usual downsides to 'cheap', generic clip tuners are the screen and the tuning accuracy. As soon as the battery is not fully charged anymore, the screen will start to flicker, which can be very annoying in a live situation.
The Polytune is a different beast alltogether. The rectangular screen is very clear and bright. Because of the colour scheme (green and red on black) it is very easy to read under most conditions. The tuning features are awesome, it has a very fast pitch grab, and the multi string function (hit all strings and the tuner tells you which strings are out of tune) is also very useful in hectic live situations. I've been using it for a week now, and can highly recommend it.