To be honest, and hopefully not to step on anyone's toes; I think there are a lot of people who are under the impression that buying the most expensive fluid is the only way to insure you get the right quality. That is a safe and fine philosophy if you are fortunate enough to have a significant disposable income. But for a lot of people, they just simply don't have the extra $100 or more it would cost to change fluid by insuring quality via just paying through the nose.
You definitely don't want to use standard hydraulic fluid (usually denoted by the "303" somewhere in the label) in your Branson as it doesn't have the required additives. But "Costco Premium Tractor Fluid" will indeed work fine with no real world drawbacks, and is about half the cost of what you can get a premium tractor fluid most other places. I am told that it does have required additives. I have used it over the years in several tractors without a problem.
My dealer, who is responsible for the warranty work on my Branson said he certainly doesn't have a problem with me using it either. Make sure it says "Premium Tractor Fluid" on the label and not "Hydraulic Oil" as some Costco stores carry both. Last time I bought it (not that long ago) I think it was slightly over $50 for 5 gallons.
I don't buy it if specs are not listed on the container. Spec I look for in my old Fords with no whistles and bells is the popular JD 303 spec. fluid, basic trans/hyd fluid. For my Bransons with whistles and bells, the popular spec. I look for is JD J20C which is the "Premium" fluid for tractors with hydros (steering and trannys), wet brakes, this and that.
Warren Co. is a packager/distributor nation wide for a lot of suppliers that carry their own name branded oils. My idea as to how they operate is that they have 2 huge vats, one filled with regular grade fluid and the other with premium, both meeting the highest spec for that grade of fluid.
Then they have a labeling dept and generic containers. When an order comes in from company X for 303 or 20c, they take a container to suit (2 gal, 2.5 gal, 5 gal) fill it with the required oil, slap the buyer's labels on it and out the door it goes.
Do you really think for one minute that suppliers, other than OEM registered suppliers, and maybe them too, have 20 different tanks of premium (for example) fluid sitting around with one made for the Ford spec, the other the JD and so on........if so, I have some Florida swamp land I'll sell you for a major housing sub division.....priced right! Wink!
I will agree that most fluids are comparable as to standard and higher quality a few of the high end fluids are definitely blended and maintained to higher standards.