Orguss1, I just started using this feature, so in no way think what I say is gospel, however, everything worked for me, and just counting down the days for the cashback from my last 2 transactions.
I for precaution, logged out after first transaction, then logged back on and completed second, but have heard of people doing multiple on one log in.
The 30% discount cannot be used on BOC weekend specials, because they are only offered through the website, and the BIN or BO is only valid on their ebay listed items which are generally higher.
The BIN quantity is good, I purchased 7 BIN boxes of 07 Leaf Limited to get the max posible on the 30% and brought the the cost down to about 65 a box.
Hope this helps