Ibex's misspelling of "zephyr" is not indicative of a systemic inattention to detail, at least as far as their products are concerned. The Zepher is well made, with tight seams, consistent stitching and excellent craftsmanship. We loved the Zepher for its decadent comfort and warmth, but we felt that the range of potential applications was smaller than with many other baselayers we tested.
The Zepher is warm. Almost too warm. The Zepher can function as a solo layer in nearly any temperature, and we often overheated when we tried to layer it. This wasn't really a problem, but it did mean that the Zepher would typically stay in our pack until the temperature dropped below zero. Essentially, the Zepher functions better as an insulation layer than a base layer.
I imagine the sensation of being smothered by chinchillas is somewhat similar to wearing the Ibex Zepher. I'm not sure how Ibex creates the Zepher's supple texture, but its results are remarkable. The Zepher has the loosest fit of the baselayers we tested. This allowed us to layer it over tighter shirts, like the Icebreaker Oasis or GT, very easily. The loose fit drew the Zepher away from classic baselayer uses. We found it more useful as a sweater than a base.
The Zepher didn't wick very well. This is, in part, due to its thickness, and in part due to the material. Wool does not wick as well as synthetic. Additionally, the Zepher is a thicker fabric than the Icebreaker GT and similar shirts, which impedes wicking. But the Zepher weathers the muggyness like a champ, staying suede-soft through the entire ordeal.
The Zepher is expensive; the most expensive layer we tested. You certainly will not regret owning the Zepher, but the dead air in your wallet may sour the tasty microclimate that the zepher would otherwise create. The choice is yours. The Aepher is a very high-quality baselayer, but there are definitely cheaper options.
The Zepher straddles an uncomfortable gray area between true base layer and a thicker insulation layer. Except in very cold or very low-movement activities, we usually prefer using the Zepher as insulation over a tight-fitting baselayer (the Icebreaker Oasis, for example). The Zepher has the peculiar difficulty of being just too warm to work as the absolute base in most instances.
Consequently, the Zepher has a useful range slightly less than that of the Icebreaker GT or Capilene 3. The Zepher is great as a secondary layer during winter activities. We'll typically keep it in our pack until the barometer drops and flakes start falling, or until we're cozying up with a mug by a fire. (The Zepher is definitely the best for lounging). We also found kayaking to be a perfect application. If you use a drytop rather than a wetsuit, the Zepher is great insulation. If you end up swimming, the Zepher will feel warm and dry long after a thinner layer would have thrown up its sleeves in despair.