It is not a matter of accuracy. All the exchanges have a price that is derived from their trades. An overall average, that is a tougher thing to find, I know that preev is there when you want a quick number and I don't recall ever thinking to myself that it was off by any degree.
It is easy and quick to load and works on any browser. I worry mainly about the prices on the exchange where my coins are. Shifting them around is a fools errand.