I didn't really care for the blade shape as well as the black and satin blade. Also it has lock stick.
That doesn't help much. As the owner of 28 ZTs and over 80 Spydercos, there are still a lot of other knives to choose from.
FWIW, I never liked the 0393; just too "busy" of a design for me. I like the 0850 a LOT but, if you don't like the blade shape of the 0393, I doubt you'd like the 0850 since their blade shapes are actually similar. On the other hand, I love the light weight and light detent of my 0850 which makes it easy to carry despite its size and also easy to wrist flick open for quick deployment.
As between the 0393 and 0850, I don't see why the Spyderco Delica, Endura, Launch 4 and BM mini-Grip are even in the conversation. These are vastly different knives than the 2 ZTs and the only 1 that comes even close is the Endura (I've got 4 of them; all of them vintage Gen 1's) but it's still NOT the same type of knife as the ZTs.
I think you need to tighten up your thinking as far as what kind of knife you really want to carry and, as others have said, you are very fortunate to be doing business w/a dealer who will ever give you a "store credit" after keeping/playing w/the 0393 for a month.
Make the right choice for the exchange and, if you don't like that knife either, do the dealer a favor and resell it here on the Exchange instead of trying to do a return/exchange again.
Good luck!