[Ed Wright]

Problem with putting it in a primary tube is, if you get something in a jetborvinjector you won't see it in your run log. With it in the collectors, you will see a lean indication. You won't know which Cyl, but you will know which bank. If it develops a misfire for any reason you will see a lean indication, but a misfire from ignition, etc) you won't always hear it at high RPM) will cause an erratic reading. A misfire causes lean spikes. Only way I would want one in a primary would be having one in each tube.
I know I don't know everything, but have been tuning EFI cars for 23 years now, and have done it both ways. I much prefer them in the collectors, at least a foot from the end.