Green lasers with the same power are I think three times more visible to the human eye over red lasers basically because your eye is far more sensitive to that wavelength in the spectrum.
Lasers can spook some animals imediately according to some on here they said Crows and magpie. I tested this theory on a crow recently, it just looked bamboozled at the ground and eventually looked round at me and gave me the "To$$er" look, but it wasnt mounted on my rifle so didnt fly off..
Dunno about Bunnies, Squirrels or Rats tho..
I use mine as a range finder and have i small graph showing what mildot or half to use depending on what one the laser falls on, works well for ranging your shoot before the fun begins. A few on here use them for ratting so yeah, go for it, just try and get a green one.