Greg; I guess we're talking apples..? I've lost track... No real 'difference' in technique, they're just more forgiving than stone-fruit. I think I've seen the "Omega" Grafting tool in action at the HOS Scion Exchange. Here again, like all 'whip to whip' grafting - matched diameter scion / rootstock is ideal, but rarely perfect enough to ignore that critical one side of cambial / bark alignment. Meaning, you will still have to align one side of the cambium, or bark of both pieces; if the other side happens to line up - all the merrier!

My concern with such a mechanical grafting device is maintaining that alignment, or keeping it from shifting in toward the center of the rootstock (or vise versa) as it's wrapped. With the hand splice, or whip & tongue I do, I'll actually tap the finale connection 'home' with a small hammer or hand pruner to a point where I can shake the two pretty vigorously without either moving, or shifting. The Omega leaves a more shallow connection and lacks that tongue (if this is the machine I envision - I've not yet searched it online). I would be extremely careful when you wrap the connection that you do not cause, or allow it to 'shift' over - and remember to wrap from the bottom up, overlapping the band a bit to create a water shedding barrier.

Scion length: If there're long, relatively large, strong roots on your rootstock, I'd leave 3 buds on the scion. If it's 'weaker,' leave only two. Keep in mind, more is not better! And of course, you could very likely get a tree by leaving only one bud, considering you'll only 'leave' one upright shoot to become the trunk. The "graft junction" you question is the limiting factor, I don't know (or think) there's a "pulling" action by the scion until / unless that graft union is established. My guess is there would be no significant difference if you were to 'create' such a 'pull' by placing a long scion - and eventually clipping it. In fact, as that clipping process would remove the end bud, the bud most responsible for giving off the hormone that drew sap past the prior buds --- you'd be weakening the scion and remaining buds...

Leave two or three buds, seal the tip with grafting seal, then leave them alone! I admit that having been one of my problems in my early days of grafting - that of leaving it alone! I'd check them daily, wiggle them, scrape bark, unwrap tape... Now they're lucky, or perhaps more lucky, that I have a hard time remembering where I put them; and by the time I run across them, they've got a few inches of new growth! --- Hope this helps