I have one complete set, brand new in the box, sitting in my parts bin. Got them for a build that never happened. I also have a front S900 on my cyclocross bike, paired with a Force rear shifter. For a 1x10 setup, it was cheaper to get a front S900 and a rear Force shifter/brake lever than it was to buy a pair of Force shifters and have the front shifter just flopping around with nothing attached to it.

Sram brake-only levers are nice and are a match ergonomically to Sram shifters, making them great for 1x10 setups. I chose the S900 to make the carbon lever of the Force shifter. I guess it's lighter than the S500 too, but whatever.