Funny, I've now moved my Lezyne mini track pump and the plastic bracket is kinda floppy so it's rattling on the frame a bit. I wonder if the carbon one would be stiffer and keep it in place a bit better when mounted on the down tube rather than seat tube.
The nylon one isn’t as open so is not as universal. The alloy or carbon ones fit any pump. I use one with a Silca Tattico no problem.