Expo Disc for White Balancing Lighting

[Marc_Bryan_Brown]

Having trouble with white balance, especially with fash gelled for tungsten to be used in mixed lighting.
Need to work fast and on the fly.
Expo disc seems like a good solution.
http://www.expodisc.com

Any endorsers?
Comparisons to Warm Cards?
Better pointing at light source or subject?
Any better solutions .
Should one overexpose a bit?

Marc

What camera are you using?

[Greg_Ferguson]

Why not try a bleached white coffee filter or the top of a Pringles can first? I use coffee filters, and have seen others suggest Pringles lids. If those don't do well enough then spend the money.

For my use, shooting in weird arena lighting on a D1X, I've found I can get a good white balance by doing a custom balance off a sheet of white paper, a poster with a lot of white in it, or the coffee filter held over the lens.

I'm sure the Expo Disc people can come up with lots of reasons why theirs is a better idea, but is it worth the difference in price?