Regarding the TK40. It's up to you if you are okay with 8 AA batteries, preferably dedicated for the TK40. For me it is fine, but to some people it may seem to be a little too much to manage and I can understand why. Especially when you need to make sure they are about the same voltage everytime before you slide the carrier into the light. I'll be very honest here..
- Max time I've used on high (277lm) was 45 mins+. The light felt a little warm. So I'm guessing it can go up to another hour or two before it gets hot to the touch.
- For medium (90lm), I've used for 3 hours continuously, the light didn't feel warm at all. So I'm guessing it can run until the batteries are depleted.
- Turbo, well we know now don't run more than 10 mins, unless there's some sort of wind to cool the fins. It was hot to the touch, but you can still hold it.

After I found out yesterday abt my LED, I did several 1-2 minutes tests on turbo at different times. LED dies are the same still, light functions are all still okay.

From my personal experience so far, the TK40 is good for any general purpose, e.g house blackouts, photography light, night walks, 1-2 days camping, hunting, work inspection, perfect ceiling light, etc. Has a very nice floody beam, because of its brightness, makes the light sorta of a thrower. It's easy to operate, nice smooth knurling, anodizing are alot tougher. After hours of usage, for several days depending, just charge the 8 batteries and pop into the light again. Simple right, it's great for any of these.

But it's not exactly, I'll use the word "user friendly" if you are gonna use it for something more:
- Long backpacking/camping 4-7 days: You don't necessarily need a super throw light for this and imagine carrying extra AA batteries (8, 16, 32?).
- Security Guard, Law enforcement: You'll be using your light everyday for hours, can be mostly on high. Charging 8 batteries or more everyday or alternate days can be tiring.
- Tactical situations: You don't have quick access to the highest and lowest modes immediately, you need to cycle thru it. Cycling thru the mode you want can be immediate or up to 8 seconds.
- Quick battery change; You'll need to insert batteries carefully and correctly. If you're in a hurry, especially if you need to run 4AA on emergency quick, you might end up putting in the wrong parallel slot, no danger though but no light! Then end up opening the light again. It's actually quite easy but these things do happen.

So there you go, these are some of the practical things I felt about the TK40 when I was using it. I still like the light though, the beam is very nice, though I fall under general purpose. It's just feels nice to hold it

Looks cool huh...