Not happy, Jan.
Dunno what the GM blades are so couldn't say. If you're happy with the OE performce stick with that, but these are about as good as it gets. They suffer with UV in the end as well of course, but they do work very well. Give them a go and see how you like them?Are they worth it though? They're more expensive than the GM blades.
Got about 18 months out of these on the Alfa, but its parked outside all the time so they get baked.