Safe Standing at St James Park

You don't get more people in, at least not with this system. For these rail seats there can be slightly less capacity rather than more as everyone has to have a seat and they sometimes remove the seats at the end of a row for extra safety.
Apparently it can increase the capacity in the stand if it is designed rather than just bolt on replacements, Everton were planning for 2 people standing per rail seat in their new stadium.