need advice on buying the right lazer sight

I'm doubting some of the ads and high prices on some of the lazer sights that are offered. It appears that the govt. limits lazer sights to the 500-680nm wavelength and to 5mw of power. It that is true then it would seem that there is a power limit on all lazers and so the cheapest one, $29.00, would be as good and as powerful as the more expensive ones. Those being $106.00 for red on up to $500.00 for green. Thanks for any help.