CO2 always works, it's what plants breathe. It's adding more than 400 ppm that requires more light and more heat to get a benefit. But even then, that's debatable. LED or HID doesn't change anything. Intense light is intense light. Many LED lamps are more intense than a 400W HPS. Many are much less.
Sometimes, running CO2 at 400 ppm is very beneficial. I'm in Canada, my friend runs at 400 ppm in a sealed room with only a 600w HPS. The lamp heats the room in the middle of winter, he's not exhausting all the heat from his house, no smell can escape, he only needs to fill his tank twice per grow. It's extremely beneficial to him. His heating bills have gone drastically down since because on top of not letting all the heat escape, he uses the heat of his lamp to heat the room. Not a single watt is wasted. His grow is separated from his house, in a separate garage.
My advice to you is to check your CO2 levels before buying anything. Most houses contain more than enough CO2 levels, and because of bad advice, people are building all kinds of complex systems to throw out all that CO2 out of their house and replace with even more complex and expensive systems. If you're growing in your home, you most likely would benefit more from closing your windows than a CO2 enrichment system. I actually have to purposely exhaust the air inside my house to keep CO2 under 1600 ppm. I exhaust the air of my grow room in my bedroom, I breathe out CO2, it goes in the grow room, plants breathe, the air comes back out scrubbed and clean. People would pay thousands for air filter of that quality. This is enough to keep a 10 x 12 room at 1500 ppm.
My other advice to you is to stop looking at marijuana specific info. It's 99% wrong. Look for advice about growing peppers or tomatoes. All of a sudden, everything is simple, clear and evidence backed.