I can't see that link (it says the product ID is invalid), but I know that measuring CO2 is actually pretty hard and requires some somewhat expensive stuff, but measuring things like O2 is easy (i believe, i'm going from memory here).
So most cheap CO2 monitors are actually just oxygen monitors that aren't actually measuring the CO2 levels but are measuring the drop in O2 levels and extrapolating from there.
I don't know if that matters for what you might want to use them for, but it's something to be aware of.
I don't have mine any more, I actually borrowed it from a friend and it was a fairly expensive one (like in the $200 range) that he was using for some other stuff.
So most cheap CO2 monitors are actually just oxygen monitors that aren't actually measuring the CO2 levels but are measuring the drop in O2 levels and extrapolating from there.
I don't know if that matters for what you might want to use them for, but it's something to be aware of.
I don't have mine any more, I actually borrowed it from a friend and it was a fairly expensive one (like in the $200 range) that he was using for some other stuff.