The Ion cannot improve anyone's putting...Things that improve putting include practice, confidence, comfortability, etc. Changing putters often gives a temporary improvement in confidence and focus that usually wears off in a couple weeks and you are back to baseline.
I could still take or leave the Ion for putting. My putting is no better or worse with the Ion than it was with several other discs. The Ion does make lighter putters better, and I may be seeing some improvement in longer putts from being able to use a lighter putter, but it would be stretch in any way to say the Ion has made me a better putter.
The Ion is irreplaceable for me as an approach disc and driver. No other disc can match it's performance in this capacity, and that is where I notice the Gyro advantages the most. It goes farther, lower, and easier than any other true putter mold (putters that are fairly high profile and glide rather than cut through the air). Old ones are perfectly neutral and the newer ones are stable enough for just about any wind. I can literally play a whole course with Ions, and they would be my one disc choice for just about any course. Since I love the Ion so much for everything else, I putt with it because I believe I can putt just about the same with any disc I feel comfortable with. It does have strengths and weaknesses as a putting mold, as does every other disc.