I'm lucky to have a good CT unit. Once tyre is properly warmed up and roll down calibrations are done it matches my SRM very well. I've tested it with 2 calibrated SRMs, and a number of Powertaps, and all within expected range of variance for those meters. I also have done multiple MAP tests with many clients and for those with good power meters we get good comparative data. I know it will manage the load increase at the intended rate, and if a client doesn't have a power meter, I know the CT power data will be reliable for testing and tracking MAP results.
The CT data is smoothed a little more than the SRM but I'm not expecting the CT to provide peak/instantaneous power spikes accurately, just manage my load appropriately, like the following snippet from a Sufferfest ride couple of weeks ago comparing CT data (yellow) to my calibrated SRM data (red):
It's an older wired SRM with no speed sensor on the rear wheel, so syncing longer power traces gets tricky as the SRM will stop recording when not pedalling, rather than when wheel stops moving. But the data maintains this sort of good agreement while ever the tyre stays warm. If I get off for a break and start up again, it'll get back to agreement within a couple of minutes of starting again.
I can imagine there may be some smaller changes in roll down calibrations for those who do extended much higher power work with low power recoveries, as the tyre temp likely varies a bit more, but for the modest power I'm currently capable of, I've got to the stage that I really don't need the SRM on my trainer bike to get data I trust for this purpose.
Having run a training centre with lab model CTs, my experience was there can be modest differences between units (I would test the different units with my SRMs), although not overly large enough to be of concern for the purpose of such training nor to feel the need to make potentiometer adjustments. If unlucky you can get a bad load gen which will be out of spec (and which the CT rep happily exchanged for a new replacement once I provided the SRM comparative data).
Despite my experience, I still recommend testing to verify the reliability and accuracy of the power data provided by any trainer (well any power measurement device really), and not to take the data at face value or rely on any claims.
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