I've had bad luck with these type of clip tuners. Is it tracking? Is it tracking now? What's happening?
This one has a clear screen that shows you immediately and clearly what is is happening. It tracks very well, but not perfectly, and generally I feel I can trust it to work and be accurate enough when performing.
The only real con I can think of is it takes a few seconds to start after pressing the button. Sometimes seemingly at random the tracking is a bit iffy, but still, it is better than any other clip tuner I've used.
It works with a bass guitar too. I mainly just use the 'normal' guitar mode for bass too, since the controls are a bit confusing, and the tracking is a bit iffy. The bass mode works better, but still not quite as good as I would hope.
I haven't found any use for the polyphonic mode. I guess it is a nice novelty thing to have and a discussion piece, but maybe think about saving your money and getting the cheaper monophonic version.
The battery life is pretty good. The screen starts flickering when the battery is running low, but you can still easily get through a performance easily. In regular use It turns itself off automatically after a while, but is not too fast, maybe a minute or two.
Overall the best clip tuner I've ever used.