My buddy just got a brand new pair of 390s, and he mentioned that the ratchets slipped as well, one time coming all the way off. He said he loved everything else about the binding, but the slip issue freaked him out.
I didn't really notice it until I went out west with them. Here in Michigan they were fine....I had to crank on them a bit, but not too bad (probably more than I should have had to though). However, out west half way down some of the steeps they would start loosening up...not a ratchet slip, but more like something was stretching. I expect things to settle in, but once they take a set that should be it. This wasn't the case. It was getting tiring...they had to go.
Maybe for a rider not pushing it very hard, they would be ok?