I’ve never been a great fan of any hardshell, and it tends to be the very last item of clothing I put on, and will tend to go with a pertex/microfibre top most of the time (either worn over a fleece, or built into the fleece/pile). But there are times when you need one, when you’re soft shell layer just won’t cope with the deluge. Seeing as I’m only going to stick it on when it’s really wet (good for digging snow holes, an extra layer when static) then what’s the point of carrying a full on shell for the small amount of time I’ll wear it?
A lightweight shell is perfect for this, and the only real downside is that a light shell will become more easily damaged, but if you’re wearing a good soft shell layer under it, then you won’t wear it that often anyway. If you’re a heavy user, then don’t complain if your shell gets holes in in, as a bit of seam grip with soon make it better again (also a few holes shouldn’t matter if you have the right stuff underneath).
As for zippers, yes I’ve had lots of half zipped pullovers over the years and really like them. For climbing any shell needs to be tucked in to your harness, so having no bulk around your waist is ideal, and a full zip is really only used because the greatest users of ‘mountain’ shells are non mountain users.
I had a very similar Patagonia top (Spectre pullover) for years, and that was ideal for alpine climbing (it ended up getting shredded by a bear!).
Venting with a pull over is the same as with a normal shell once it’s tucked in a harness or rucksack strap, and often the baggier cut of a pull over can allow better convection cooling.
I guess Mountain Hardwear’s pullover range is based on Ueli Steck’s design feedback, and I suspect that it’s so perfect for climbing that its manufacture comes from the marketing budget (I argued for this approach to niche climbing products when I worked for Berghaus) as its just so uncommercial. Generally when you see a great pullover (or any great climbing product) you need to snap it up - as they don’t stay on the market long! (the Montane Spectre Smock is very interesting example of a great smock).
So the answer is… yes get one before someone at MH realizes there aren’t many customers like Ueli!