Cheap circular polarisers
I have tried some cheap ones that were complete rubbish.
Normally I use Hoya pro digital or kenko pro
However - my favorite is a 'no brand' from India bought off ebay for about £4 .
So - despite the rule of thumb - you sometimes get lucky

Carl
No matter how many lenses I have owned - I have always needed just one more
For most situations though, the Hoya is the clear winner.
Regards
David
Flickr
Nicola's Apartments, Kassiopi, Corfu
Some cameras, some lenses, some bits 'n' bobs
Aero
Member
Aberdeen (Scotland)
Al