I bought some earlier this year. I have used it in a flintlock, works well. I ran some test loads with it over a chronograph and posted the results here - Post#337300
As you can see from that post, Express ran about 120 fps slower than the same load of Swiss. When both of them cost about the same, it appears the Swiss is a better offer.
There was some controversy here about what Express was exactly devloped for, as a muzzleloader powder or as a cartridge powder. Some of Goex's early advertisment led one to believe it worked in both environments. I don't know the answer there other than to say it performs flawlessly in a clintlock under a PRB.
My overall assessment - Express is not worth the additional expense as it is only marginaly better than regular Goex which can be almost 50% cheaper be pound.