Hmmm, interesting. I think I know what you mean by "grab," but I look for it more in gels than leave-ins. That's why I love Aubrey B5 Design Gel at the moment -- it grabs onto the curls while you scrunch it in, without causing your fingers to stick to the curls (causing frizz), as so many gels do.
As for leave-ins, I know what you mean by too much slip. I almost feel like too much slip can decrease curl rather than encouraging it. But what I look for in a leave-in is not so much a "grabby" feeling -- more of a mushy, squishy sort of feeling, because it helps clumps to form. But maybe that is grabbing the hair -- just in a different way? Lately I'm really liking GDLI for this. My old favorite, BWC leave-in, is starting to seem a little too slippery these days, by comparison.
Wurly and proud!
Modified CG since 2008.