I'll have the Kirk vs. RRS decision to make for a 1D X L-bracket. In the past, there have been some minor differences in terms of which had a slightly lower profile, etc., but they seem equivalent in terms of quality and price.
It may come down to who has one ready first. If at the same time, I'm inclined toward the Kirk, because RRS sells only direct while B&H distributes Kirk - means overnight vs. cross-country shipping.