I have researched CO2 exhaustively...there is a wealth of information in the marijuana growing world...and it works. In fact some intensive lighting systems for marijuana are not recommended without the addition of a CO2 system.
While visiting Sam Tsui during his last couple months in business, I recognized a C02 burner hanging near the ceiling. I asked him about it and he gave me a brief instruction on usage and offered to give it to me.
C02 burners and generators are not expensive and you could even use C02 from a welding supply business. The harder and more expensive part is the measurement and control system.
I could install a C02 system in my GH for under $2000...it would be an extravagance that would only work from about November to somewhere around March, because the GH is basically a closed sealed system...Outside of that time period, vents and fans are being used to control temperatures.
In the marijuana growing world C02 is used indoors with LED lighting and climate controlling systems keeping temperature parameters in a zone.
I have thought that when a grower (orchids) is producing excellent plants, surely "culture" is key, ppm fertilizers used, and very possibly C02. Tokyo Orchid Nursery...Hmmm. Sam Tsui used it!
I believe there is a benefit, how much, Im not so sure.