I had a quick check of the Zens and they have magenta coloured coatings on the objectives, greeny on the prisms, and a bit of a combination on the oculars. I have probably photographed them way back when and posted them on the ED3 thread.
The colour representation seems pretty neutral to me, if anything the transmission peak seems to be in the very bright green region. I have noticed that the blue colour (as on a Superb Fairy Wren etc) seems a little weaker than on other bins I have seen - such as a Zeiss HT or Swarovski SV for instance. I wouldn't call the Zen colour rendition warm by any stretch.
The ED3's use 2nd generation Vividbrite dielectric prism coatings of 40 layers. It is interesting that the 3rd Gen coatings used on the new ED4 are still 40 layer.
I didn't notice any significant differences between the Bushie and the Zen, but the day was quite dull. I know that of a late sunny afternoon my two eyes have very different colour casts anyway - one blue/green, the other golden/orange - this is very distinct and kinda cool
The Bushie tested on Allbino's certainly has a pretty nice transmission curve that bins 10x the price struggle to better, and as to my knowledge no-one has actually seen a transmission curve for the Zen ED3, I would say they would be identical. Can anyone confirm for sure the number of layers used in the Bushie M's dielectric prism coating ??
I much prefer the ergos and particularly the focus speed of the Zen - they are pretty much perfect. I use the thumb indents to brace my thumbs crossed over from the opposite hand (I comfortably hold a 50mm SV), and also find this a super stable hold. I also like the smoother contoured (and unarmoured) bridge of the Zen which I rest my middle fingers on - this gives me absolutely zero gap between focusing forefingers and gripping middle fingers (puts the Zeiss SF to dog-legged shame! :) - the next two I have wrapped around the barrels.
The Bushie is definitely a different (though derivative chassis). The focus wheel I tried had a small amount of backlash of a mil or two. From conversations with Zen-Ray it seems that those that exhibit more tension (stiffer focusers) correspond to less backlash, and vice versa. At least my unit has a nice light smooth focus! :)
I didn't pay great attention to the standoff of the eye cup rim from the ocular lens on the Bushie, but that of the Zens is absolutely minimal - any less and the surface of my glasses might risk contacting the ocular lens. When checking the distortion of the Bushie I could pretty much see all the field, so the difference is not great (I didn't pay great attention to that either as I was marking time until I could get my hands on the 10x SF.
Overall, I wouldn't necessarily say the Bushie is an 'upgrade' to the Zen. The different body and smaller slower (jeez, that would really annoy me) focuser may be more conducive to better backlash tolerances. As you and I have both noted, unit to unit variability is going to play a part in both brands. The eye cups of the Bushie may also suit non-spectacle wearers better, but that's as far as I would hang my hat on differences going.
One thing is for sure, that even if the Bushie's ergos run 2nd to the Zens (for me), if you can get them at half the price ~$200 you are getting a great buy !