@pyna,
The sc5 version is noticeably larger in the head. It will not feel as minimalist compared to sc53 series, but you will get better output, throw and heat management. Both are nice and different enough to maybe warrant having both
I'll second that. If you're going to stick with AA batteries, then the SC5 makes for a nice outdoor compact light. The extra throw is very useful, and the extra brightness helps a bit (though it's not a huge difference). IMO, I don't find the smaller SC53 much good outdoors. For a headlamp, the H53 makes sense (though I prefer the H600Fc).
I don't use my SC5w much anymore, since I much prefer the SC600w HI for outdoors. But it's 18650 based.
Because allowing protected 18650 won't hurt. For you, you can still just use unprotected 18650 and forget about the additional ability.
I know it's not needed for sc600, but my point is why strip that additional ability? It's perfectly possibly that a customer may have a huge light in parallel to one-cell sc600. Fenix tk75 for example, which requires button top.
Also, sc600 does take up to 6volts, at least for the earlier generation. So just extending that tube a bit longer, we can use two cr123a in emergency situations. No H1? Fine with me. My current outdoor system: a 18650 light (Fenix tk15UE), and one super light-weight h32fw cr123 headlamp, 3~4 cr123 batteries as backup. See? Nice and neat, cold temperature ready. If I were to use sc600 in lieu of tk15UE, I need to pack an extra 18650 because it doesn't take cr123s.
Zebralight's niche is very small, bright, and efficient lights. Sticking to flat-tops allows them to do that as well as possible.
Sure, allowing protected cells and CR123 doesn't sound like a big deal, but it forces the light to be a little longer, and possibly a bit thicker. They also then have to worry about protection circuit tripping at H1, or people complaining that it won't work on H1 with CR123 or that it drains the CR123's way too fast.
You could pick up an older (and larger) model if you really need cell compatibility for emergency use. Those support longer cells, but I'm not sure if they do CR123 (other than the SC32 of course). If you're using it for emergencies, then the extra brightness and new UI of the latest models probably doesn't matter to you.