So I'm about to pull the trigger on this lens but already have an f-mount 400mm f2.8. I'm wondering if there are any advantages to the 180-600mm besides zoom range and not needing to use an adapter. I had the f-mount 200-500mm for a while and thought it felt very cheap in comparison to my 400mm 2.8. Particularly, the tripod foot which was terrible to use unlocked on a tripod. Not smooth at all, and very clunky. Is the tripod foot of this new lens Z any better? It's not an s-line lens which also has me worried.