On Timesaver, I recently used this to lap D valves and valve seats dead flat. Yes, their literature says the abrasive breaks down under use, which is what I found, I had to "freshen" or completely replace my puddle of timesaver + oil. They have a yellow grade for brass/bronze, and a green grade for steel/iron, the instructions clearly state to never use the green on brass or bronze.
I've not yet tried it on steam, but at 100 PSI of air there is no leakage. I was impressed.