Though American brown ales are made with chocolate malt, I prefer the British brown ales; I've used up to 50% of this brown malt in my all-grain malt-bill - the results are fantastic. There's no other grain or sets of grains that exactly duplicate the flavor of this british brown malt.
This is the stuff if you want to brew an authentic English porter.
Just brewed a London porter (trying to clone Fuller's porter), with about 10% brown malt in the grain bill. The beer turned out very close, and I'm pleased. I don't think you can get the right flavor profile without brown malt.
I use this in my London Porter recipe. Unique tasting grain that can't be duplicated. Has a rich grainy, roasty, slight coffee taste that can't be beat. Roasty but not harsh. I like it so much in my Porter recipe that I use 10% for a sold punch of rich flavor. You can use less of course around 5% at first to see if you like it, or go for it and enjoy!