BSAC is the recognized national governing body for dive training standards in the UK and elsewhere. It's run like a non-profit club, but it's members run it through an elected board, similar to NAUI. Also, BSAC diver training standards are recognized by other agencies, and therefore indemnified.
A "GUE Open Water Card" may get you air at a particular dive store, but it won't be the basis for obtaining continuing education through most diver educational agencies. You might as well show up at my shop and ask to take an Advanced Open Water course showing a card printed, "Bob's Dive Training", diver #34 - my insurance won't allow it. It wasn't too long ago that PADI and NAUI did not recognize each's training standards.
I'm all for getting great diver training from any source... just don't allow the pretences of others to become yours.
Which is sad, because I think that GUE and UTD would produce better divers than your typical PADI/NAUI. I've seen a UTD Rec1 cert dive for OW and those divers are far better than most PADI/NAUI rec divers I've dived with even with 100+ dives, and their associated instructors and DM's. That is in skills and performance, not experience, of course.
But there is a tech slant to each. UTD considers open water what NAUI Intro To Tech might be. So there is a bit of disconnect in terminology and purpose. In my mind, UTD is a bit more modern and in touch with newer and better practices but UTD is very heavily "team" oriented. Moreso than any PADI diver I've dived with.
case in point, I often dive with people that have no idea what their air is so I have done now 4 OOA assists (one was a near drowning at 92 ft. and not my buddy, this was a rescue, not OOA assist). Others, after working with them in a training capacity after OW, have no clue what their buddy is doing. Sometimes they descent without agreeing first, and descend not even facing each other, then when they reach the bottom, instead of asking if OK, they each go their seperate directions then look for each other.
I'm not going to knock any agencies, it is clearly the instructor's fault for not hammering it home, but some agencies are more prone to allow this kind of behavior reward with OW card than others. GUE and UTD would never allow it. So from that perspective it could be agency related.
There is very few NAUI shops around here so I have yet to come across a NAUI OW (I am all NAUI from OW to Master Diver and soon DM) so I can't comment. Everyone here is either UTD or PADI. There is a stark difference between the OW between the orgs.
My point being is that it is sad that PADI or NAUI wouldn't recognize a UTD or GUE OW cert, becuase the abilities of a typical OW from those orgs would far surpass those of the typical NAUI and PADI. That is why you pay so much for PADI, they want a dollar for every time you think of hopping in the water.