Power level choice is a bit tricky on these things - you want a visible beam even in clean outdoor air, so you need a fair amount. On the other hand you are standing out there in the dark with probably fully dilated pupils, so the chance that accidental exposure would do serious damage is a lot larger compared to the same power leven with contracted pupils in a daylight environment.
These things don't combine well, you need to somehow safeguard that noone can be hit by the laser beam or even a reflection off it from something like a window.
520 nm is a good wavelength though as it is very visible for a given power level. 532 is a tiny bit better but with dpss lasers you get temperature issues, sometimes emissions of 808 or 1064 nm light that is hardly/not visible but yet damages eyes and such, so the direct diode is a better choice.
