I also have a 4.25" ATI. The frame to slide fit is real nice. The rails are not sloppy and the rear of the slide matches nice to the receiver, the beavertail to frame fit is smooth. Very well fit considering the price. The springs were weak in IMO. I installed Wolf springs new out of the box...
ATI 4.25
Here's a couple shots of my 4.25" ATI. I decided to try doing a bobtail using an Ed Brown MSH. I had to refinished the receiver after. I used Wheeler Ceramic-coat. The slide and other parts were still in the original parkerized at this time.
Later I decided to lower the ejection...