I was previously using a Nikon T-ring adapter from one of the cheap Amazon sellers, such as Astromania or Svbony. I’d recently noticed some aberrations in one corner of my images while using the Baader coma corrector. After playing around a bit, I found that the cheap T-ring adapter didn’t fit tightly in the camera, and had a bit of slop in and out. I supposed that this may have caused the slightest amount of tilt of the sensor, and caused the coma corrector to not work flatly over the field. I’ve since bought a new Skywatcher Quattro coma corrector and their matching M48 thread T-ring.
This adapter is a much tighter fit, and I have found no play in it at all when attached to the camera. Definitely worth the little more in price to get a better field!