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.