At the grafting class I took this spring, they had fancy (and expensive) tools including the Omega, but the experienced grafters who were teaching us preferred to use good grafting knives. I made a total of 5 apple grafts under very close supervision using both a knife and the Omega; none of which have survived. (But I think it didn't have as much to do with the grafts themselves as the scions and rootstock.
I know enough about the techniques now that I'm going to order a good knife.
I use a cheap omega tool from Lee Valley. I grafted a good number of pear, apple, peach and plum, with better than 60% success. Plus, it was the first year to graft anything.
This is my grafting page: http://www.diamondjfarms.com/Trees/graft.html
I also took a grafting class. It was after that class that I knew that I would not be able to get those cuts just right, and it sent me looking for the grafting tool.