John, we just bought a duplex and came from a regular FC2. First I would agree with Adam that your probably not going to come in at 22 ounces with the platinum.
As far as durability the CF might be a little more delicate but probably not much. The FC2 is pretty delicate and the platimum more so. Much of that depends on how rough you are on gear. The materials themselves are not apples and apples so you have to look at the longevity reports to see if they jive with your expectations. If the duplex actually does last the equivalent of an average thru hike I will be thrilled. I also don’t know what the longevity of our BA tent would be. I guess that would depend on how good their fabric coatings are in general. As far as quality of build I would rate them both very good so far.
Now when discussing livability the duplex comes in far above the FC2 . The wife and I are about 5’8″ and the duplex is a palace in comparison. Where the FC had barely enough room to squeeze in sleeping gear and emptied packs at our feet the duplex has a ton of usable space at the head, foot and above. It offers plenty of room for sitting up, all our gear comfortably inside and the two side doors are sooo nice for rolling out of the rack. The only drawback to the extra room is that I can actually misplace stuff inside :)
The duplex also beats the FC hands down in set up. I pitched it once in the back yard for kicks before our first trip and was amazed at how easily it goes up. Much faster than the double wall with poles. On our first trip with it we were pitching it in a fraction of the time of the FC. Its so easy its like cheating. Now if you have some bad staking conditions it would be more time consuming gathering rocks or other anchoring materials.
One concern of ours was the size of the footprint. The FC is great in the tight spots but we were able to pitch the duplex in a couple challenging spots with no problem so that’s a non issue for us.
Packability goes to the duplex as well. One piece fold and roll and your done. No breaking down and stuffing poles, one piece instead of 3 and one less stake to carry. Yes cuben doesn’t pack as tight but comparing the volume of the two mentioned shelters they are about the same in.
Where I feel this shelter will really shine in comparison is setting up in the rain. Much easier to pitch the duplex than setting up the FC in reverse. Condensation is a concern of ours but the duplex vents so well with all the door options it may be more of a fear than reality.
When getting back into the sport we started with the FC and I have no regrets as it was decent shelter had at a great discount which allowed me to purchase a lot of other great UL gear. At the time I didn’t give a hoot about the limitations as it was a fairly light shelter split 2 ways. Now that the wife and I have renewed our commitment and love of BPing the added expense of the zpacks shelter is proving well worth it. Time will tell but so far the comparison is not even close.