Regarding V and Z transformers, I have found them usually quite reliable and since they have a higher output voltage range, they are a necessity for running older Standard gauge and AF wide-gauge steamers, also prewar Hudsons perform better with a Z. I was unable to run a fully-lighted Railchief set with my ZW, but no problem with the Z. The down-side is the lack of reverse and whistle features. This makes them less desirable and sometimes hard to sell. The ZW will always be the most popular postwar transformer because of its features and its "sexy" throttles.
I am having a problem with a V. It was rebuilt long ago, I think by Ken Koehler when we were in the Chicago area. It must have a faulty/wear circuit-breaker, because after a few minutes running a single train or even just for lighting, the red CB light starts flashing and the output pulses, eventually trips-off. I have worked on ZW's but not the V or Z types, so it will be a new experience figuring this out. I am hoping I can just replace the CB. Too bad that Ken K, Mr ZW, is not still around.