I only use metal curries to clean brushes. I don't use metal anything on mine, I grew up with my mom preaching at me that metal curries/shedding blades/sweat scrapers dull and break the hair.
I love slick & easy blocks (but buy large blocks in bulk at food supply stores - get 10 out of one big grill block for a couple bucks instead of $5 a piece) At that price, I don't care if they get nasty & full of dirt, I just take the rasp to the edges and file off until new and toss them when they get too small.
I'm also a big fan of the Shop-Vac. By far my favorite grooming tool :) I got a groomer's rubber curry attachment for it at a garage sale, my gang loves it. Before the attachment I'd use a rubber curry and just brush towards the vacuum hose.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.