ive always used the GD0600, it was a little tricky at first, buts thats the only one ive learnt on. with a little control ive made Uro on smaller trees with it too, but the dremel is probably better for refining and smaller work. GD0600 is superb for block carving, large hollows, removing wood fast. i find that the motor goes on dremels far too easily. i cant remember if the 603 was available when i bought mine or i might have got that one instead, its the equivalent to what G potter and Kevin wilson use in their videos, the 906.
this hollowing was done with a 600 and a terrier bit,
20180509_160656 by
Bobby Lane, on Flickr
touched up with a wire brush on a dremel
20180509_160707 by
Bobby Lane, on Flickr
2018-05-09_04-13-59 by
Bobby Lane, on Flickr
personally i find it very smooth to work with, no kick back like ive sometimes found when trying to block carve with a dremel. this tool doesnt faff about.