I had a Manix 2 (for a short period of time), I actually bought it alongside a Griptilian. Both knives were smooth. While the locking mechanism on the manix is stiffer, the blade glided open and closed like butter. Once you have the technique down, there is no problem. Either is a solid choice, it comes down to personal preference. I ended up selling the Manix not long after.
The Grip's stock scales were okay. Nothing structurally or functionally wrong with them, and I don't see them breaking anytime soon. But I traded for some Cuscadi CF scales and it feels much more solid now. Peace of mind more than anything else.