All Helium-Neon (or HeNe) lasers have a required warning label on them.  This states a number of things, including listing a power level.  This power level will almost never be the actual output power of the laser.  Companies will not print up a new warning level for each model -- they will print up a few different ones with maximum levels.  A 6 mW, an 11 mW, and a 12 mW HeNe laser tube might all come with a warning sticker that lists 15 mW -- or even one that lists 20 mW.  A 5 mW warning sticker could be on a tube that is factory rated for 1 mW.

So first off -- that warning label power level means very little.  Many sellers will use it as the power level in their auction, and it will be a false claim.  It's like claiming a car can actually do 140 MPH because the speedometer goes that high.  Always check the maker's model number.

If it is being sold as a used laser, there is a reason.  Many times it was swapped out when its output power fell below a certain level.  That laser with the 30 mW warning sticker and a 21 mW factory power rating may only be putting out 11 mW by now.

Lastly, if it really puts out more than 5 mW it isn't a toy.  You can blind yourself or others with it.  Don't be an idiot!