In reply to galpinos:
I saw one back at the IPSO Trade Show, but haven't actually used one unfortunately; either way, my thoughts were much the same as yours.
Unlike the Hirundos, which actually has a good/solid feel, the Sitta felt like it was constructed using significantly lighter weight and thinner materials - so much so you can actually see through it! As a result I, like you, was a bit surprised when I saw the weight difference was actually quite minimal.
Either way, I personally tend to favour a bit of extra comfort/durability over weight anyway. As a sweeping generalisation the lightest things tend to wear out the quickest, what I liked about the Hirundos was that it actually had a good balance on that front.