Saving peoples lives and contant income?
Yes please
You won't be saving many people's lifes as a retained firefighter, you will however go to many afa's (automatic fire alarms or automatic false alarms depending on your point of view) jobs where you don't do anything, leaking radiators, bin fires, car fires and other uninteresting jobs. Ocasionally you will do something that is worthwhile but not very often. I would imagine also that being self employed you will get frustrated at the ineffeciency and missmanagement of the fire service itself.
As for the constant income depending on how your fire service operates you may be paid a retaining fee every month, paid for training evenings and then paid whenever you get a call out so this can vary greatly from month to month.
Some services pay a salary every month for retained which can be good for quiet stations but not so good for the busier stations because if you had alot of call outs in a month and was away from your window cleaning alot you would get the same money as a quiet month where you were able to get on with your own work.
Others things to consider are being called out at any time day or night, having to plan when your looking after your children as you need someone to look after them if your on call and get called out.(i know one guy who sometimes when his wife went out to work hired a baby sitter while he was still at home incase he got called out.)
There are positives as well otherwise i wouldn't still be a doing it but don't do it to become a hero with a constant income.