Don't forget that the owner of GUE is also a PADI instructor, and he has PADi instruction offered at the shops he owns, so that agency should be avoided. I wonder what it is like instructing under those circumstances. How do you remember whether you are supposed to be God-like or incompetent during a class?
But mostly that is not the case. For a random customer, choosing a random shop/Instructor the outcomes will be different, on average, between GUE affiliated shops/instructors and PADI ones.
For instance, there is a difference in rules about whether an instructor can be in teaching status. One of our localish GUE instructors is currently unable to teach as he is busy getting on with other parts of his life and cannot meet the minimum requirements to continue. He will have to jump through some QC hoops to restart.
The dedication required to become, and maintain, GUE instructor status is not the same as for a PADI instructor.
Quite often we have people come to our club who did a course in some warm water resort location. Because they are the market leader the diver is likely to have trained with PADI. We say ‘excellent, we can start with the Sports Diver course’. Sometimes they say ‘hmmm, I would rather start from scratch’.
So while there exist some fine PADI instructors, and I have trusted my son with one (although she also teaches TDI and BSAC), on average, you are likely to be better off elsewhere.
Size is a disadvantage after a certain point, at least from a customer point of view.