OAT anti-freeze price / help

Has anyone found OAT anti-freeze cheaper / better than this?

Millers Oils Alpine Red Extended Life

5 Litre costs £13.49 + postage from Bosch Batteries UK

Link here:

http://boschcarbatteries.co.uk/index.php/millers-antifreeze-extend-red-5l.html

Also do I really HAVE to drop the plastic undertray to drain the radiator?

Can't you just pull the bottom hose off and let the water run out the bottom of the tray ?
Its only like going through a ford ( all be it a shallow one)
and when you go up a hill whats caught in the tray will run out the back, although some smart person will undoubtably say " Oi mate there's water running out your motor"!