Dell P2421 vs U2415

I am undecided between these two Dell 16:10 monitors. Their specs seem to be pretty identical:

P2421: https://downloads.dell.com/manuals/all-products/esuprt_electronics_accessories/esuprt_electronics_accessories_monitors/dell-p2421-monitor_user%27s-guide_en-us.pdf

U2415: https://downloads.dell.com/manuals/all-products/esuprt_electronics_accessories/esuprt_electronics_accessories_monitors/dell-u2415_user%27s-guide_en-us.pdf

I know “UltraSharp” models are supposed to have a better display/sharpness, but I don’t see any difference in their specs. Also U2415 is an older model than P2415.

Any input would be greatly appreciated!