I bought some today, and come to think of it, I'm taking it back. Would rather spend the extra on synthetic than to do a "trial", with possible results being, "well...I have a definitive answer on the 80w85w-90 Napa Ashland Diff oil, and I need to rebuild my rear end now"...but that's just me. I'm not much for "trial" to save maybe $15, with regards to a $1200 rear end, and the word "trial" in one of the above posts solidified that for me.
There's my useless opinion. Hey, it just occured to me...that's what we're all here for, to exchange useless opinions!