CO2 bag, anyone try it/is using one?

Saw this "co2" bag at the grow store last night; I asked the lady about it and she said: "Just hang it in your tent under/near the light, when your light comes on it warms the bag and creates "CO2"."

I see a lot of ppl using co2 tanks and stuff; but what about this bag? Is it worth it? I'll be using a 4'x4'x72" tent.

I have a exhale in my tent.went from brown to white in about 3 weeks.to be honest I have no damn clue if it is or did work at all.

When i bought it, they said its for small grows. i used it in my clone tent. (36x36x20). I dont know if it worked but my clones looked really happy! $20 for peace of mind...

ya a lot of people dont really know if they work. someone with a co2 meter needs to measure it and find out what the output is. they are best used in small grows although i dont see a reason you just cant keep adding more of them until you get a good c02 reading in the room. i have one and i notice the plants it would be dropping co2 directly down on use more water. thats about all i can see as far as showing its working. more co2 lets plant use more light which then uses more water?? idk lol