55lbs in a 10bbl batch (11.5bbl knockout) will give you a strong impression of the malt. More than this is overwhelming. For milder flavor use 1/2 this amount.
It is like a dark toast flavor showing up in the aroma and aftertaste. It gives this style complecity. I feel it is a defining element in a brown ale, along with caramel malts.
As far as malsters, I have liked all the English producers of brown malt i have tried.