They do not need CO2, that's a myth supported/promoted by many to have a fully planted tank.

I helps produce more growth, but it's not required, it does make you do more work though.

They just need to add a good substrate, have a reasonable fish stocking level, no plant eaters, and pack the tank and do a few minor things from there.
They work very well.

Most CO2 folks do well with the non CO2 approach also.
If they try it.

Regards,
Tom Barr