Converting 3d Printer to laser engraver

I am doing some research on converting my 3d printer to a laser engraver. The conversion seems simple enough but I am between two types of lasers. I do not know much about lasers other than the higher the MW the more powerful the laser. I am currently looking at these two laser modules

http://www.gearbest.com/3d-printer-parts/pp_368053.html

http://www.gearbest.com/3d-printer-parts/pp_501984.html

One is a 5v 1600mw laser and the other is a 12v 500mw. Does the difference in voltage change anything? even though the 1600mw is the higher power laser, does the lower voltage change anything?

Thanks.

You need to know the wavelength of the laser, and the properties of the material you intend to engrave. Some lasers will have no effect on some materials.

If those are 450nm, they'll be good for most opaque materials, but I don't expect them to work on polycarbonate or acrylic. Longer wavelengths are only good on darker materials. Shorter wavelengths are good even on many transparent materials.

It is more important to get the right wavelength; a less powerful laser with the right wavelength can be used more slowly, but a more powerful laser with the wrong wavelength will just be ineffective faster. :)

Both of these lasers are 450nm. I dont intend to use it on acrylic, mainly on wood and materials of the like. So does the voltage matter for these situations? or is it just the mW of the laser that matters with the amount of power output?

With all other things being equal, more power (mW) means the same work can be done faster.