Yeah, don´t use the GW-tool. I´d argue that noone should buy any hobby-materials from GW, since there are cheaper and at the same time much better substitutes to be found elsewhere. It is not a bad tool per se, but the two tips it has are not that great to work with for most applications.
My favourite tools are these:
1: A skull that I recently sculpted, using only the following tools. The skull has a heigth of 5mm.
2: a pointy tip, with a flat back.
3: Much the same, but with a rounded, flat tip. I use these two the most, hands down.
4: Clay shaper cone. Its a rubber tip that is great to work with. Useful for soft lines.
5: clay shaper, tapered tip. Like teh above, but with a pointier tip.
IMO 2+3 are the most versatile and useful basic tools.
Your problem with the sticky green stuff is a common one. Keeping the tool moist is the simplest solution, but you could even use vaseline. Do not press the tool into the clay, but drag it lightly over it, to smoothen the surface.
Another tip: Mix the two phases and let the Green Stuff sit for about 5-10 Minutes. It should have lost most of it´s stickiness but should still be pliable enough to work with.
Or you go ahead and purchase ProCreate, another 2-phase epoxy clay, which is much alike Green Stuff, but does not stick nearly as much.
I hope this post was of some help.
Greetz, the Maniac