I would humbly request, if you can even find an extinguisher that uses it, to please avoid halon. The substance is an extraordinarily efficient ozone destroyer, and has been pretty much banned.
As for CO2, if you’re going to use it, please get training. The blast issued forth from a CO2 extinguisher, if improperly used, is likely spread embers all over the place an create a larger problem than you started with. Imagine expending your one extinguisher on a fire, only to have four more light off from smoldering embers a few minutes later. Also, if you’ve never used a CO2 extinguisher (also with many other dry powder extinguishers, but especially CO2), you’ll be particularly surprised by the static discharge created when you discharge it. It’s important to keep the canister on the ground when you discharge it, to give some of that static a place to go. Otherwise, you’ll feel quite a bit like Luke Skywalker looked during his run-in with Emperor Palpatine at the end of Episode VI. --it won’t kill you, but you’ll definitely not need that kind of surprise when you’re already dealing with a fire.
I’m going to go out on a limb here and just suggest a box of baking soda be kept nearby. For a small fire discovered in the small’ish enclosure of your new GF, you’re not going to want anything propelled under high pressure. (Fire extinguishers have all of that force to allow you to go after a fire from a safe distance of several feet.) If something catches alight inside your GF and you’re not comfortable simply reaching in to put it out with your hand, you can safely smother a fire with baking soda. Baking soda works through two effects: first, you can smother a small fire with a pile of baking soda; and second, the heat of any remaining embers actually cause the baking soda to break down and (gently) release carbon dioxide, further smothering the fire by displacing local oxygen. It’s really wonderful stuff. You can simply vacuum up any remaining (after you’ve allowed the pile to fully cool. There’s no need to turn your vacuum cleaner into a home afterburner demo). It’s non-toxic, as are it’s breakdown components. (Commonly used in cookies! yum!)
All of this discussion, of course, goes with the assumption that you were present either at the moment of the fire’s ignition, or very soon afterwards. This requires always babysitting your GF when it’s operating. If something catches fire inside an unattended laser cutter, eventually leading to the whole thing being on fire, then you’ve got a combination electrical fire, burning plastics fire, and heaven knows what else. That’s where you’ll want your large ABC extinguisher and a call to the local fire dept. At that point, the laser cutter is likely to be a total loss and you’re just trying to protect the surrounding building/business/domicile/workshop/etc.
Being a bit of a high school pyro, as well as fire fighting training in the Navy and prior to wintering in Antarctica, I’ve got a healthy respect for fire, and a (perhaps at times annoying if you ask my wife) paranoia about things unexpectedly catching fire. Enjoy life! --but try to enjoy it without being on fire.