Originally Posted by SteveinA2

Buying Premium Economy and upgrading to Club can often be a really bad deal compared to advance purchase business class with no miles or using a few more miles for a straight Club AVIOS ticket. So check the fares carefully before you commit.

TBH I did PE purchase and miles upgrade once over Christmas as there was a PE sale...so it can work, but more often its an illogical way to go if it is your money buying the PE