You can etch on to metal surfaces with a CO2 laser but for many metals you would have to treat them with a coating for the laser to be able to etch because of the reflective surfaces. You certainly will not be able to cut metal with a CO2 laser found in most of the smaller machines but the larger ones use what I believe is callled fusion CO2 where oxygen is used while cutting, very expensive if you want to cut sheet metals then a fiber laser, pulsed Nd:YAG, laser will be required, also very expensive. These types of lasers will generally etch metals without needing a special coating as well.
I can't really comment much on the metal cutting lasers as I only use my 100w laser for etching metal, wood and glass and cutting ply and acrylic.
Trotec lasers have a good reputation but I have no experience of them.