Actually, Kendall GT 1 is a 229.3 oil (MB Specs)
Mobile 1 0W-40 is 229.5
Not really the same properties. Not that big a deal in a Ford, like it would be in a Sprinter, but there's a difference in the properties (other than merely the weight and viscosity). The MB Specs, while mainly meaningless to a non-Mercedes vehicle, do apply to the oil itself moreso than the vehicle, so they can be very helpful in determining what a particular oil can and cannot do, what it's properties are, far beyond the simple weight and viscosity numbers and API classifications.
Kendall GT 1 is a higher ash oil, for example, than Mobile 1 0W-40 or Mobile 1 5W-40 (Delvac). The Kendall oil has the same properties as some of the Mobile 1 SuperSyn oils, like the SuperSyn European Car Formula 0W-40, and the SyperSyn 5W-40 and 5W-50 oils.
Basically, all oils that meet the same MB specs, regardless of brand, will be priced about the same. It's not really about advertising (contrary to popular belief, that's not even how advertising budgets work, anyway), it's more like all 229.3 oils will be priced the same, and all 229.5 oils are priced similarly. The SuperSyns and the Kendall are priced about the same, for example.
Main thing is, since engines wear differently with different brands and types of oil (I cannot stress that enough), pick an oil that will do what your engine requires, and stick with it. Don't be changin' oils just to be changin' oils, or worse, 'cause one is cheaper. You will get what you pay for.
Kendall GT-1 is a very good oil, and will give you about a 1% increase in fuel economy over a dino oil. So will all other 229.3 oils. The 229.5 oils will give you about a 1.8% increase in fuel economy, tho.
I'm a big proponent of synthetic oils for a lot of reasons. They give better fuel economy than dino oils. They have significantly longer invervals between oil changes (229.3's like the Kendall are rated for 15,000 to 20,000 miles between changes, and the 229.5 oil can go up to 25,000 depending on gas or diesel), therefore, the longer you can go between changes, the fewer chances there are of any of your oil finding its way into a landfill somewhere. Not to mention that the longer you go between oil changes, the less foreign oil you will be using.