Well, given those parameters,
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Unless you've bought a bigger machine than a Kombi, beware the 300mm blade. It's a millimetre thicker, far heavier, and probably too big for a Kombi. I bought one, and it takes too long to spool up, and too long to slow down. I'd expect concerted heavy use to damage the drive line. If you're meeting a post every few metres, loop handle all the way, for precision.
Basically, as far as I understand, it's because you don't have the same control over the machine. Just imagine trying to cut the hedge face vertically with a bike handle strimmer. The idea doesn't appeal to me.