I tried these for the first time today and I must be doing something wrong because:
A) I could barely do 3/4 of what I can deadlift as far as weight goes
B) I barely felt them in my lats/back (Cephalic_Carnage had suggested shrugging backwards at the top, which I forgot to do, so that may fix this one)
C) They hit my glutes so bad I couldn't walk for 3 minutes after one of my sets. They still feel like jelly now.
D) I tried to keep my shoulders back on them but if I was doing more than about 135 they drifted forward a bit...not a ton, but still.
E) I tried to keep my lower back in a tight arch, and now my lower back is killing me.