I’m assuming this will fit the C8 and many S-series lights. 8A is suitable for the SST-40 and SFT40, but will likely be limited by forward voltage with most emitters.
5A is running a 519A, SST-20, etc… fairly hard, while 3A is a pretty average single-emitter light.
I wish they had these available couple of years ago; I moved all my self-assembled lights to 21700 Hosts because cheap buck and boost drivers were only available in 20mm and 22mm sizes.
I haven’t been building a lot of DIY stuff lately, but I have a C8 I think is going to need one of these and the upcoming high-CRI SFT40.