Never used one when I shot FTR but trusted the results and the rifle. My ES was 6FPS (finally measured by 2 different magnetospeed chronos) and yes, if you attach anything to or touch a free floating barrel with anything, it will affect the harmonics. How do we thing barrel tuners work?
With high performance rifles anything you can do that reduces the time between changes is a bonus. Dont sweat the stats, they will as likley be different between days and groups. Just get out there real time and see how they perform on paper, thinking about the marksmanship principles and consistancy. And work from there.