I need to get a core drill. I was looking at the Dewalt 21570K - has anyone got one? Are they any good? Or should I spend a bit more and get a Marcrist DDM1? I'll mainly be using it to cut holes for 100mm ducting. I've seen a post on here extolling the virtues of the Marcrist DDM2 but they don't seem to be available anymore and are a bit out of my price range (I don't want to spend more than ÂŁ250 and ideally a bit less than that).