Yes they are very good. Far quicker then a normal pump. However most people usually carry a small pump with them as well as the c02 to get the tyre started. And once you get home you should deflate the tyre and re inflate using a normal pump as C02 leaks.
Look on the net for C02 pumps to see what takes your fancy. They all do the same job at the end of the day. Just that you may want a simple one that discharges a bottle in one go or one that has a controlled discharge.
You can get the bottles for an average of about 90p each.
Also check out the search box on these forums. There are a good few threads asking the same question.