That valve looks like it would work for your paintball co2 cannister.
Though as you mention a on/off valve, not sure if you mean a solenoid type set up, this would indeed make life a lot easier but these tend to work mostly for dual gauge regulators.
I used to have a single gauge reg on a small cannister, it worked fine but it is annoying to set it on to required level in mornings or afternoons and turning off in evenings every day turned to be a bit of a chore.
Since I did a DIY reg with a co2 fire extinguisher with a dual gauge regulator with solenoid, life was so much better and plants did take off pretty well as long as you have decent lights and adding a daily regime of ferts or EI ferts, then you're good to go.
Pretty much common sense required here and missing ferts once or twice in a while does not do a lot of harm but if you regularly miss dosages then plants and specially algae will let you know :x