I use soft shackles and woopie slings for years. I have never had a failure, or one slip. I would be very surprised if either way was slower, just what ever you get used to. I have mine up as fast a a cinch buckle set up. I like it better because no sharp or hard objects to deal with. It is a very light set up as well when you are concerned about weight as well. But in the end I think a lot of it is simply personal preference.
I recently made some SS's and tried them out in my front yard, then on one AT hike. They held just fine.
However, it takes two hands doing fine work to open and close the SS's, whereas the MSH doesn't. Plus, the MSH is faster to put up and take down. I have used the MSH for a couple of years now with no problem.
So, I'm going to experiment another time or two. But I'm not convinced that SS's are better than MSH's and may switch back.
"You can stand tall without standing on someone. You can be a victor without having victims." --Harriet Woods