Thanks for the replies. Please don't think I'm trying to 'have a go' or be deliberately derogatory about the club shop, but I'm sure you must appreciate as a first purchase and as something as safety critical as wiper blades, it doesn't look good!!
I'm happy to offer as much info as possible to help the shop resolve the problem, in particular if it isn't just a one-off bad set of blades. Unfortunately, I suspect it is more likely a bad batch of inferior rubber.
Before I return the blades, I'll make a little video of both types in action and post it here to show what I mean. It will also demonstrate what I mean about either blade missing part of the screen.
Thanks