How are you growing? Hydro grow can benefit from added CO2 more than organics in soil. Personally have never used that product. If u are just doing a few plants indoors in soil AND u have a decent amount of air turnover, than I don't think you would benefit from adding CO2 at all. On the same note if u had a big hydro setup you want more CO2 than a product like that could give you.
Don't let the grow stores sell you stuff ya don't need, they will try.

My 2cents.
Hope helps