The only real way to know if they are good or bad is to fly with them. If they work, they are ok. If one does not, throw it away no matter if it glows or not. Easy enough.

And yep, probably a good idea to keep them in the package to show they are new. But, as many RC'ers do, I keep one or two on the plug tool in the threaded holders provided. Easy access. However, I also put the old one back in the hole rather than throw it on the bench and leaving it there (forgetting about it). Then next time, I look at the plugs on the tool and wonder what ones are good and what ones are bad.

CGr.