I had a chance to put the U13 to work in real environments and am really happy with it. I took it to a grassy knoll that is above an old elementary school that I routinely hunt. It has a good mix of modern/old targets with the oldest targets being 7+ inches deep. There's not a ton of trash here, maybe trash/targets every 15 inches of swing or so on average. I have hunted this spot THOROUGHLY with the D2 and haven't pulled a silver out of this spot in many months, so I felt it was a good spot to test the U13.
The U13 had no problem hunting this spot and that extra 3" of coverage really made swinging a breeze. I immediately noticed that I was getting a significant number of deeper targets. Ignoring all shallow targets, the first deep target was 8" VDI 76-77. It was a warped copper button top from a two-piece button. Second target was 9" really faint high tone whose VDI bounced around, but the tone stayed high. This turned out to be a wheatie.
Pinpointing on the U13 is better than the D2. The D2 is not the best at pinpointing to begin with. I still occasionally have a target in the side of the hold with it. The U13, surprisingly was spot on and I felt like I could dig smaller diameter plugs.
I ran into a few spots where the U13 could not separate and I had to change my angles. Those spots had targets that were approx. 3-5 inches apart. Two of those target clusters were crap-shoots and I could not get a reliable read on them. It makes sense that a 13" coil would have trouble with 3" separation though...
I spent a couple hours here digging various deep targets, mostly relic/trash. No silvers, but I am not disappointed because that tells me that the D2 got most or all of them!
Summary: In my opinion, the U13 is a great coil, slightly better than the D2 when used in non-trashy areas. I really look forward to re-hunting some other locations with it. This review is also a testament to the D2! The D2, imo, is the best all around coil for the MXT for those who seek old silvers. I'll say it again that if you already own the D2, there's very little reason to get the U13 unless you hunt a lot of open/non trashy space. I wish I had the U13 when I hunted Germany last year and you can be sure it will go to Europe with me in the fall, along with the D2!