It's tough to separate training agency (GUE) from gear manufacturer (Halcyon) when they were started by and are owned by the same person, especially when they were both developed out of the needs of specific cave diving projects. Oddly enough, they tried going to Scubapro to have them make the very specific gear that they wanted and Scubapro responded by saying there's no market for it so Halcyon was born. (Now Scubapro has a backplate and wing system available - guess there was a market after all.) It also really doesn't help when trying to separate GUE and Halcyon that some of the people who are attracted to the high quality training standards and high quality dive gear unfortunately sometimes come with a very large ego. Because they have invested as much time, money, and effort as they have, they have a very strong sense of pride which feeds that ego and then leads to them insisting that GUE is the only agency that matters and Halcyon is the only gear you can dive.
As with any training agency, the agency can't really be held accountable for the personalities of their divers. It is responsible for their dive skills but personality and ego are things that a dive agency simply can't fix.
There is no requirement to use Halcyon products for GUE courses and no requirement to take GUE courses when you buy Halcyon products despite what people say. Is it more expensive? Yes, mainly in part to quality and also that they don't outsource parts or labor overseas.