I don't know about the aftermarket stuff, but the original OEM ZX sensors are a little different in the way they mount... On the Z version, the brass body portion is all one piece and the electrical guts are crimped to the body to finish the assembly. In contrast, on the ZX version, the tightening nut spins independent of the sensor body. The "body" portion is two distinct and separate pieces.
Why does that matter? Because if you use a ZX version with the spinning nut in a wet location like the Z thermostat housing, it will probably leak through the seam between the body and the nut. You could probably use a Z version in the side hole in a P79 or P90 head, but I would be wary of the converse of using a ZX version in a Z thermostat housing.
That pic above of the aftermarket ZX sensor looks like it's made pretty much the same as the Z version, so who knows?
Oh, and the connector key is in different locations between the two of them. Not an insurmountable issue, but something to be aware of.