I think they were orignally designed for similar posts, what the Yanks call T-posts. Clipex is good stuff, I do a fair bit of it. They've taken some time to get the UK products up to scratch, but are getting there now. Had many problems with mis-spaced slots, galvanising tolerances and the like.
I bought a petrol driver for Clipex, but on chalky ground it's no use. Even after pilot drilling with a 1m long 22mm SDS drill, it struggles and it's quicker to use a mandraulic driver. Just not enough weight.
I've just bought an Atlas Copco LPD-T,. weighs in at 33kg, so should be much better, might even do scaffold poles into chalk also. Fingers crossed- it's due sometime this week.