Ok, I will first say this is probably the cheapest, and brightest green laser you will get.
The pressure switch has given others, as well as me problems, it just seems to work shortly...then a connection somewhere gives out. On top of that, the laser is brighter with the tail switch anyways.
If you plan on using this with the tail switch, which can be pushed for momentary, or twisted for constant on, then its a great buy.
This laser is big, so I wouldn't recommend it for a pistol, to get an idea of size, I'd say length is about 2.5 cr123's, and about %50 wider than them.
I mounted mine on a rail on a MP-22(or AR-15, in 22 for those who dont know).
Zeroing is fine, the problem, due to the size is that you will get "cross over", meaning that if you zero at say 50 yards, the laser will be off (either up, down, or side to side) depending where you mounted it. It will also go off as distance increases beyond your zero. If you have a mil-dot scope or similar, you may be able to get the laser parallel to one of the mills, which could be useful, say, you would always hit 2 inches high.
Other than that, its great.
One last thing, this is bright....very bright, so bright I fear it may cause splash radiation, so I'm very careful as to shining it on reflective objects around the house for example.
It shouldn't cause permanent eye damage...but it is made in china.
Great buy overall, would rate all 5 should the pressure switch be better quality.
Pros: Very B...