Nope, its one of these old wives tales a bit like you have to use the offical site to pull NOTAMS so that you are logged as reading them.
A complete load of bollocks before the internet.
And now the internet is here even more so as the amount of international sites that proved metoffice data without all the nonsense that you have to go through to get it on the metoffice site.
The vast majority of the flights flown in UK airspace the pilots have never looked at the metoffice.
It seems stupid that the majority of UK pilots use third party and wx providers in the USA, scandinavia, and flight planning intergrated options with no logging jsut because the home grown offical site is a royal pain in the arse with poor graphical representions of the forecast.
Yes I know they say that feedback is positive about the new site. I would say thats because most have given up using it and can't be bother giving negative because they just get what they want from other sources.