I personally have not run the light long enough to notice drop in output (only use it to find a keyhole at night occassionally) but as PhantomPhoto says, I don't believe the light is regulated.
I don't usually wave the light around (any light for that matter, but I have never really needed to) so I have never experienced this stroboscopic effect. For normal use such as walking with your light while lighting the path or simply pointing the light at an object, I have not seen any flickering, strobing, etc.
There are different lights for different uses, and A3 and K3 are just general short-term use keychain lights for me. A3 just increases the versatility with the multiple levels.
FYI, my favorite "key chain" is the free one I got from Lighthound when I ordered some products through them. It has equal or maybe even better output than K3, easy to operate, durable, and smaller than K3 or A3.
By the way, that spot to focus on K3 is really useless, imho. First, it's too easily moved (slight tap will move the head around). Second, with the given output, at close distances, it really doesn't make much of a difference.
Just my $0.02. Hope this helps.