That's the FERM one I've got (and from the same seller) and I'd recommend it over the Dremel any day. It's every bit as good and less than half the price.
Having said that..... I prefer the dremel's way of driving the flexi-extension - it's a bit simpler and more elegant than the Ferm/Clarke method. It's not enough of a difference to justify the extra cost though as the Ferm/Clarke one is perfectly adequate.
Iain