A friend lent me a Z-4000 to test as a replacement for my old ZW. My trains ran great, but the voltage from the two accessory outlets is very low. My accessories ran too slow and layout lights were too dim.
I ended up getting a great deal on a ZW-L from another friend that purchased it with a collection. It has variable voltage accessory outputs like the old ZW, so you can adjust voltage to your liking.
This isn't intended as a "knock" on the Z-4000. It's a fine transformer. It's also much cheaper than a ZW-L if you don't get lucky like I did. I just want to point out a deficiency, in my opinion, with the Z-4000.