HAHA I know what you mean, someone here recently in another thread said that they have never seen a straight beam. I can't understand any excuse for such poor craftsmanship.
Alex, the 520nm diodes are less efficient than others and do produce more heat, it is quite possible it really does have a duty cycle of 2 minutes. It is normal for it to start dropping in power as you exceed the duty cycle, it happens on my 520nm, I can see it if I measure it on the LPM, it is common to all solid state/diode lasers, there may be some that low power with no duty cycle but probably not a 520nm.
Alan