I have three Colortunes, used simultaneously. For optimum results you do need to do a little seat-of-the-pants fine tuning after setup as Ray says, but I’ve found they do a decent job of getting the mixtures close.
We got into this discussion back in ‘14. The conversation got to be a little more animated when the reference to Colortune in the manual pictured came up.
Essentially, the author recommended jacking up the rear wheels and having an accomplice simultaneously apply the throttle and the brakes (in gear, of course) whIle you fiddle with the mixture. 