I'm confused by the "at no cost" comment I've seen a few times about adding a 2nd user.
Adding a second user for an individual account holder
http://ibkb.interactivebrokers.com/article/1004 says at the bottom:
In accordance with market data vendor requirements, the account will be assessed a separate market data subscription fee for each user account added. In addition, user account market data subscriptions are tied to and cannot vary from that of the account holder.
So, whatever you already have your primary account, gets doubled onto the 2nd user.
I suppose it would free if you weren't paying for any real-time data, but that would seem unusual.
Not a huge deal, and I get the benefit and almost necessity; but, please clarify if I am misunderstanding.