whoopies will be adequately strong, as long as the burys are an adequate length you don't have to worry about them slipping under normal load. if you're trying to see how short of a bury you can get away with, that's a different story.
the advantage of the adj web suspension is mainly that's it's all one piece rather than 3 pieces, so you don't have to worry about walking off with one or both straps still hanging on the tree, and the setup will be a little faster/easier for most folks for the same reason (1 piece vs. 3).
whoopies will reduce bulk and weight, just depends on how much you care about 4-5 oz. and a little bit of extra pack space.
paul at arrowhead is currently selling these new buckles, they are not yet avail for individual sale on my site yet.
I am also just a little curious about worrying about the whoopies. I think that it is good to play with different systems to see what works best for you. Lost of people really like whoopie slings, but I have sold tons of buckles and rings so I know that lots of folks use them still. But not sure why the apprehension over whoopie slings, the more you weigh the tighter the bury constricts, the more hold they have. I have had almost 600 pounds load on one for 24 hours with no slippage BTW.
Anyone of you can easily change my mind by sending me a whoopie sling in the mail.. pm me for shipping info and i'll consider changing my mind about them