I have a Zone VI 10x8 ultralight the latest design which I got used. It is very similar to a Wisner traditional in every respect apart from materials. I dunno what others are like, but mine is well made with very accurate machining indeed (I have heard them slated constantly). Materials are very light so do not have that robust feel of heavier wood and brass (mine is aluminium), but I suspect force required for breakage would be enough to make any camera need a trip to the repair man

It is rigid enough, in that force required to 'flex' it would translate into a very strong wind; strong enough to induce enough vibration to prevent shooting anyway. Final point tho, is that whilst functional I have no emotional bond to it as it is not beautiful and does not have the slightest bit of personality like something hand made. I can deal with this just fine if the images are great tho

I wanted light weight and used value. It is certainly light and being virtually unused, good value.
Having handled Wisners and various others and owning an ebony, the Ebony is simply leagues above the rest in quality. The Wisner to me felt positively home made and crude in comparison. The exceptional finish, function and rigidity of the Ebony products is constant both across the range and from example to example. I have never heard of a 'dog' tho of course the odd fault gets thru like any product, tho rarely. In the US I feel that the Mahogony RW45 with universal bellows to be by far the most appealing std 5x4 folder on the market and I would not entertain the idea of anything else of similar cost such as the Zone VI or Wisner, personally.....to me there is a night and day difference in quality. Having said that I have seen some 5x4 Zone VIs go VERY cheap used, even when 100% mint ($350). Ebonys hold their value too well for good used bargains it seems.
Tom