It is easy to work with, and I have tested it using browsershots. Displays correctly in almost all browsers. My only concern is the load-time. So far it does not seem too bad.
I've been really impressed with flex charting and if the 300 bucks isn't too much for ya, I would recommend it. Google finance is a good example of it's power and integration ability with javascript.
FusionCharts is good, well documented, and damn cheap (but not free). They do offer a fully functional trial version-- it just has a big "demo" label on resulting flash graphs.