The Terrain’s instruments include an oil pressure gauge and a temperature gauge - which could save your engine! Often ‘idiot lights’ don’t warn you until damage has been done. The UX does not have an oil pressure gauge.
The power windows standard on both the Terrain and the UX have locks to prevent small children from operating them. When the lock on the Terrain is engaged the driver can still operate all of the windows, for instance to close one opened by a child. The UX prevents the driver from operating the other windows just as it does the other passengers.
Both the Terrain and the UX offer optional heated front seats. The Terrain Denali also offers optional heated rear seats to keep those passengers extremely comfortable in the winter. Heated rear seats aren’t available in the UX.
The Terrain offers an optional 115-volt a/c outlet on the center console, allowing you to recharge a laptop or run small household appliances without special adapters that can break or get misplaced. The UX doesn’t offer a house-current electrical outlet.
The Terrain Denali’s optional Automatic Parking Assist can parallel park or back into a parking spot by itself, with the driver only controlling speed with the brake pedal. The UX doesn’t offer an automated parking system.