I put in 4 side grafts last year and they were probably the most vigorous grafts I had. I grafted directly to the trunk in the vicinity of other scaffolds. There is a side grafting thread here with more info. As mentioned in the thread the main issue for me is the angle of the scaffolds that are created. They are naturally narrow so the longevity of them may be questionable. I was able to pull the limbs down to encourage fruiting but it didn’t change the crotch angle. Just an experiment for me.
Here is the thread on Side grafting