No, I don't think titanium is a good idea for flashlights.

Yes, titanium has a relatively low density; that is, compared to the iron or steel that would be used as structural metal instead.

But most metal flashlights are constructed of aluminum, which is actually less dense than titanium. It's also a better electrical conductor (used for the current's return path). Aluminum is also much easier to machine and to work with in general, and an order of magnitude cheaper. Both resist corrosion quite well, but especially aluminum, which forms a thin but nearly impervious layer of Al2O3 on its surface.

So unless you spcifically need the added strength that Ti provides above Al (and these uses would likely already be using steel), using Ti is counterproductive.

I'd never buy a titanium flashflight. Its aluminum cousin would be just as capable, effective and durable, and probably weigh less to boot. And it would sure cost a hell of a lot less.

Still, it might be a nice marketing gimmick for someone trying to sell crappy flashlights at high prices. Nobody knows a damn thing about titanium, but as soon as you mention titanium, people buy the things up like it has some kind of magical power.

Titanium, like iron, various carbon steels and stainless steels, aluminum, copper, brass, bronze, silver, gold, lead, tin and so on, has a list of unique properties that suit it to certain applications.

Aluminum gets a bad rap, but it's pretty damn good for a huge number of things - it resists corrosion exceptionally well, can be easily machined, is quite light and offers a great deal of strength per pound. And pound per pound, aluminum is a better electrical conductor than copper, silver or gold (you just need larger diameter wires, but they still weigh less than narrower copper, silver or gold wires of the same resistance.) In fact the primary drawbacks of Al for electrical purposes is that it's harder to solder than the "noble" metals, and that it is less ductile than the same.