I have heard many times that the datalogging from the RT gives false data on the Lightning computers. The only thing worse than no data is bad data! Save the money and get the regular version.
Yes, you can turn off the CEL from smog removal with it. I don't have a computer with me that runs the software to tell you exactly, but under the scalars there is an EGR option. I believe it even says in the description to change to 2 to turn off EGR. Once turned off, no more CEL!