CO2 is no more dangerous than the 180 litres of water sitting in your living room. Like anything in your kitchen, if you keep things out of the way then youre not going to have your kids fiddling with it. As already said, the only real dangers with CO2 is the cylinder falling on someone small.. even if it leaked all over the place its not going to really do anything to worry about.. the amounts were talking about in the 2kg FE's is comparatively small.. the small 600gram JBL canisters are tiny (and consequently dont last very long before a refill!).
however.. its not essential that you use CO2, there are other ways of adding organic carbon to the tank.. you could add excel, a liquid additive from Seachem. Your success with such methods are going to be relative to the amount of light you have over your tank, and what your trying to achieve.
You need to remember the following formula: light drives CO2 intake which drives nutrient uptake which drives growth.
The more light you have, the more of everything else you need.
If youre going to run a high tech tank, with good amounts of light, then yes, you'll have to add CO2 and have a good fert dosing schedule such as the 'Estimative Index' (EI). If youre going to go for a low tech tank, then you might get away with excel and moderate ferts such as the liquid feeds from Seechem.
The best thing to do is read up on the forum to get a feel for what you want to achieve, and then try to pic the technology that suits that aim.
If youre after a full, lush growing carpeted tank in not very much time, then youre going to have to look at CO2 and a high tech tank. If however youre prepared to take things slowly, then maybe the other option will work for you. Bear in mind also that an EI schedule is a commitment in time.. weekly water changes, daily dosing and ALOT of pruning as things will grow like wild fire.
Anyway, whatever you choose let us know! Everyone is always very interested to follow someone elses experiences
everyones tank is different, we all learn a great deal from each other, no matter how little any of us think we know
its one of the things that makes this a special place.