Here's my take on "slow turn" or "no slow" or whatever the latest marketing gimmick term that shops are using:
As far as I have seen "real" users report (and not the companies selling slow-turn fixed controllers) the issue only affected Halo series of games. I had some customers report the problem onf "CG1" style controllers. I never had any customers report the problem on "CG2" style controllers. I offered to customers to pay shipping both ways to get my hands on a slow-turn controller, but at the same time I made that offer, my company had switched to CG2 controllers, and we never had any more reports of problems.
The slow-turn fix involved taking sandpaper and making the hole around the joystick wider. What really should have happened is the game developers of Halo should have fixed their calibration numbers, or, allowed users to run a calibration routine with their specific controller to solve the issue.
This "bug" in Halo as I would call it, spawned an entire industry of "no slow" fixers, selling controllers at $20, $50, sometimes even $100 markup for doing nothing more than using sandpaper to increase the size of the hole around the joysticks. Some companies didn't even do anything to the controllers at all - they would just go through a pile of controllers, testing them using an "app" on XBOX Live, pick out the units that did not have the slow-turn problem, and then sell those - selling the units that did have the slow-turn problem as "normal" controllers or selling them on e-bay to unsuspecting buyers.
There is an app on XBOX live still that will let you check the "range of motion" of your joysticks, but the app doesn't necessarily mean anything because each game developers can use their own calibration or range-of-motion for the joysticks to ensure no problems with "slow turn". So if you run the app on XBOX live to check your range of motion, the results may be inconclusive. I still see mod shops out there today guaranteeing against slow turn - which is great, except it's just not a problem. What's actually more of a problem is the :censored:ty quality of MS joysticks lately, and the "drift" issue... I'll leave that for another post some day...
If I am wrong, somebody let me know, but I'm very much a "proof or it didn't happen" kind of guy, so I expect some current data or up-to-date youtube videos from somebody showing this problem in action on a new controller. I sell thousands of controllers every year, if there were some slow-turn epidemic, I would be hearing about it from my customers, but I haven't had a complaint about slow-turn except a complaint about Halo 3 and it was waaaaay back in Fall of 2009 when CG1 controller technology was still circulating.