Hi!
Being able to measure the ppm is certainly helpful if there is a problem or you want to push the plants hard with nutes and need more accurate info. Personally, I think your plants look fine. If you don't want to bother with the ppm, I say don't unless your plants give you a reason to. Someone who tests ppm religiously though will probably disagree with me.
Edit: Oh and I meant to add, I'm totally going to look up that CO2 box you have. I have 10 bags of Reishi mushrooms sitting 2 feet from the closet with my autos and can make more in hours. I'm intrigued!