Well, 5mW 650nm is not eyesave for direct exposure, even if it’s less than a second.
If you can make sure noone can get behind the laser to look into it, you should be finde.
5mW would be plenty for a dot, propably to bright to look at comfortably , but as a line I guess it should work great.
Perhaps an expert can correct me but this is what I think I have learned:
To look directly into, 5mW is considered the damage limit, as long as your eye-reflex closes the eye within the normal 0.2 seconds. When unresponsively flashing around a laser for fun the time that it flashes into a eye is much shorter than. 2 seconds, so you get away with at least 50mW. Reflections, apart from mirror-like surfaces, usually are quite harmless, the light is scattered too much already.
One should know that the cheap 5mW modules/pointers are often WAY more powerful than 5mW.
I have some 5mW cheapos and an expensive/normal priced 50mW and some of the 5mW are more powerful than the 50mW.
From what I know about laser’s the IR is whats considered most dangerous to the eye. A cheap laser will have a high IR and a quality laser will have a low IR. Its already been mentioned above but most china laser’s are under rated and part of the reason that they are more powerful is they have a high IR that is also calculated in the mw rating for output. If you filter out the IR the laser will lose some where around 25% or so, depending on what you buy. I would try a quality laser that’s rated at 5mw with a IR filter. The green laser is also much more visible in lighted room. The eye is much more sensitive to green light.
I think it is not a problem, if they are under powered when in use (with line generator), because it really does not need to throw far.
I also think, that we can install it to the machine so, that we will get the best out of it even if it’s not that powerful.
We have one “safe” laser line generator on other machine to which we can compare. If it seems to be too bright or annoying, we will trash them and get better ones for the purpose.