Is a madridsta membership worth it? Real vs Celta Vigo

Me and 4 friends are travelling to Madrid next weekend and want to attend the Real Madrid v Celta Vigo match.

What is the best way to go about this. Is it worth buying a madridsta membership for one of us and will this let us buy 5 tickets? Or are we ok to wait till the general sale. We are just worried that tickets will sell out before we get a chance to buy them with the queueing system if we wait for general sale.

Thanks