Probably the bigger sights. I found it easy to get headshots with the QBB because of the big reticle.I don't but it's not really the fact I'm not scoping quick enough, it's the fact I can line up shots easier with my no land beyond right now than my HB.
Sounds weird saying it but I kinda want an NLB now. Sharded the one I had the longest a long time ago and many many times before, now I've been wanting to try it out lately.