jarledb: You should also be aware that the powder is very fine and that it gets everywhere after you use it.
When you add in that the powder is corrosive and will damage electronics after a while... It can get very expensive if someone sets it off without there being a proper fire.
Foam extinguishers or proper fire hoses are good alternatives, and a fire blanket is good too.
One good reason to stick with powder is that it lasts for 10 years, while a foam extinguisher only lasts for 5 years.
CO2 you really shouldn't have in your home, unless you intend to use it on your very expensive Hi-fi or other such electronics. The CO2 will be useless in a fire with any real amount of energy (so fire in wood etc. it will only have a short and temporary effect).
Fire hose? Who wants a fire hose in their house?
I would recommend having a look around, Mitre 10 sell extinguishers. Choose something you are happy with and that fits your budget. Fire blankets are cheap as is a bag of flour for cooking fires.
At the end of the day having something is better than nothing!