Originally Posted by DrIsotope

I imagine part of the reason is that SRAM uses DOT fluid, which rules out any and all Shimano calipers.

If weight is your overriding concern when it comes to braking,
flat mount Shimano 9170 caliper, 123g
flat mount Hope RX4-SH caliper, 109g
flat mount Hope RX4-SR caliper, 93g
...and the post-mount versions are even lighter.

I personally don't care what it weighs. Any weight savings are a nice bonus.