I wouldn't recommend that if you want a good quality <5mW pen. Those could be 15-30mW, mode hopping, the brightness could go in and out, not worth the hassle. Stick with the 635nm from O-Like as previously noted. You can find it here.
I'd actually be interested in building you a safe, low-powered under 5mW laser pen (I can guarantee safe output with my laser meter). I've been wanting to build it for some time now in this gold-plated pen (reasonably priced), check your pm.
I think this will fit teachers/professors perfectly