The Nettars are generally really well-built, robust cameras. I don't know what Zeiss did differently in their bellows manufacturing from other companies, but the bellows on these cameras seem really resistant to developing holes.
The Vario shutter was the low end and relatively simple; if I remember aright there are no slow speeds, which means fewer things to go wrong.
Terrific cameras. The f/6.3 version of the Novar may not go wide enough to show the serious vignetting that happens at wider apertures---it can be a very likable effect (as long as you know to expect it). The 6x6 frame is small enough that the corners won't get seriously blurry, but as with any triplet, you should expect some dropoff in sharpness away from the center.