I have one S1, and use the A6 as my EDC. The moonlight and turbo shorcut make it a wickedly useful-lived-experince light.
S1 has slightly nicer anodising, threads differ between the two, and just checked side by side that the driver and interface are identical (in behaviour at least). I just kinda prefer the A6 for some reason (maybe because it says BLF?). I only use 18650 so shorter tube is moot.
It’s my default “best possible value” gifting flashlight for friends and colleagues who go to work in challenging places around the world.
A6 is generally cheaper, so for me it’s a no brainer to buy the A6 @ ~18-20USD on sale, either the 3D or 5A depending on use case (3D for indoors, 5A i think gives better depth perception illuminating green things like trees and grass).
I can’t think of a better budget EDC, but i won’t stop looking for one!