The battery level indicator light for non-rechargeable flashlight

My initial thought, a battery indicator light does make the light look fancy and a bit more attractive, also, it sounds like it do make sense. Yet, do I really need it in real daily-use?

If I use the light around my home, I don't think I would care the battry level.
If I would go out somewhere for some days, I would charge the battery to full and bring the backup one.
If I go out to walk my dogs, yeah, I may want to know how many battry left. But I knew I shoud change the battery if I turn it on and it just conldn't work or last on the highest output.

So, it turns out to be not as necessery as it looks like. It may make the light more complicated and less reliable in the end. And I guess all I need is some low battery warning so that I could change the battery before the light dies out. For a indicator in a rechargeable light, at least I could know how much time should I wait before it fully recharged.

I'm with you - I can take it or leave it.... but mostly the later.

They do make sense for running Li-ions, where voltage is a good indicator of remaining capacity, and the nature of a protected Li-ion is all-or-nothing (ie, full output, or tripped protection circuit). But voltage from NiMh's doesn't really tell you that much - my SC52 shows full (four flashes) on a 2/3rds depleted Eneloop. For NiMh's, I often just compare my two highest outputs.... when I lose max, I know the cell is nearing the end. My primary lights tend to be efficient low/sub-lumen lights, so even with a 90% depleted cell, I know I still have a day's worth of useable light. Course, I also carry a AAA back-up light, or two, and never really needed to use them yet.

An internal battery meter would be fine by itself, but I really don't like the idiot-proof auto step-down features they're often paired with. The SC52, for example, won't support one of my favorite cells - the 3v lithium primary CRAA/14505 - and probably LiFePO4s as well. Battery meters also seem to require electronic switches, which I'm not too fond of for the reliability reasons you mention. Electronic switches add yet another point of failure (and anecdotally, seems like there's plenty of posts of them), are not field serviceable, by-passable, or Lego-able (like mechanical clickies) and dedicated manufacturers of them (eg, ZL and Spark) tend to offer sub-standard warranties.