Hey there. So, I tried answering this earlier but I was banned. So here's round 2.
I've invested heavy into co2. And when delving into that. You really don't wanna go cheap pal. As I suspect. That you just don't wanna know your levels but are looking to enhance them. Well, say you get a meter and it reads 1500ppm and it's over 5000 cause your plants are locked out of photosynthesis (which if you don't have the right environment extra co2 beyond ambient level will just increase and increase and be deadly in the environment. Co2 stays low to the ground so, any pets small kids and so on, are the 1st to come into contact.
So, I would highly suggest you spend more or close to 200e on a well known brand. So many reviews I seen on amazon with meters giving much lower reading that what was really there.
My pro leaf. Its one of the best on the market that doesn't cost as much as the Eco / growtech but just as good. If not better you'll find they all use parts of the same reg vivoson. It'll set u back 290e can go up to 500$ on some sites.
You'll get a fuzzy logic controller that reads co2 by the second. And is as safe as they come. If there's a fault. It turns off.