NiCopp is very forgiving, so I bet you had good luck with that style tool. I've fought with and broken those working with steel lines so many times. I started using Inline flaring tools, and will not go back.
I've been using this one for years, but recently bought this one so I can do multiple sizes.
The gates belt that I tried split from the front edge into the center of the belt, then split lengthwise about 3 inches then the rear half broke. I could see wear marks on the front edge of the first split. Like yours the rest looked fine.
Never had a Dayco belt break, but the bearings in their kits only last a couple years.
Since it disappeared from the USRM twice, and I've received a few PMs asking where it went, here it is. Still in the same place as its always been.
---begin USRM cut
http://random.removed.us/altswap.html