I own, and carry a ZT0400 quite often. It can be closed with one hand easily. Upon disengaging the lock, you can use your index finger or swing your thumb around to the spine. I wear XL-XXL gloves, but I`m guessn any size hands can do it with practice.
The ZT0400 is a great EDC knife for those that want something larger. The tanto and recurved belly is a turn off to many, for me it was. Until I started using it more. The tip is great for pickn, pokin and pryn. The recurve excels at pull cuts, and open push cuts. I don`t recommend it for cuttn your steak and potatoes during dinner.
The clip side is smooth, the trac-tec is only on the front handle and provides great grip. The handle is shaped very similar to the Kershaw Shallot, only larger. And, IMHO, the AO operates like a Shallot, in that it requires much more force to open, meaning closed blade retention is very strong.
I carry mine tip up, it rides well at around 5oz, slides in and outta the pocket very smoothly, but at the same time, the ZT clip is strong and secure.
A very underrated model in the ZT line up.