I downloaded the file "V20t-DEC-20-2013" which was 50,76 MB successfully using mobile 3g network, but after the phone restarts and begins the updating process it gets stuck at 3% ang gives me an error. Then it reboots and gives a message of the device being suspected of root.
used the site a couple of times myself for my E975 and then flash the whole rom.
because i never had a problem, but maybe it's just different in some countries.
but if you decide to use LG's flashing tool remember to backup your data on your computer, or else they will be lost because LG's tool formats the phone totally.