Just wanted to add my experience on 2 occasions:

May 2016: CGK-SGN-LHR
Got an email saying "Upgrade to Business accepted subject to availability - ask airport staff for final confirmation".

Check-in staff at CGK were useless, had never heard of Optiontown and thought I was crazy. Eventually got to speak to a manager and with some computer magic, a boarding pass for the first leg was spat out. Couldn't print the second, so told to go to the transfer desk in SGN. A nice first flight with plenty of wine. Upon arrival at SGN, I was advised at the desk that J was now unavailable but they would upgrade me to Y+ instead, the man spoke excellent English and was very apologetic. 3 days later I got an automatic refund from Optiontown (so the Y+ upgrade on second leg was free in effect, I just paid for the first upgrade).

November 2016 (last week): KUL-HAN-LHR
Got the same email saying "Upgrade to Business accepted subject to availability - ask airport staff for final confirmation".

Check-in staff at KUL had a list of Optiontown customers (just me and one other on this flight), no problem at all in printing both boarding passes. I was told they weren't supposed to give me lounge access but if I picked up the invitation left lying on the counter, they wouldn't stop me unfortunately the first leg was delayed, so didn't experience the lounge in HAN, but the whole Optiontown experience was a lot smoother compared to my first one.