Hmm, they claim 1200 PPM in a 12x12x12 area for up to two weeks. Thats impressive. Of course the area has to be well sealed. If you are venting to cool the area then you will just blow out the CO2 as fast as it's generated.
I've done a good bit of research and recently added TnB to my garden. Grow boss on you tube has a pretty good video for evidence on how long they last. My plants seem to be loving it so far.