Why buying a Dev Kit?

I want to develop an app. What does the Dev Kit offer that I can’t simply do with the normal version at half the price?

The dev kit was mainly to make development possible in countries where the retail glasses weren’t on sale yet, since you can only get the retail glasses from a cell service provider, and as such it would be locked to only certain phones sold by that provider (usually a 5G phone since they like to market the NReal glasses as a reason for 5G). If you have access to retail glasses and one of the officially supported phones, those are better for app development than the dev kit.