1920 × 1080 vs 2560 × 1080
Full HD 1080p against UltraWide FHD, side by side.
2560×1080 renders 691,200 more pixels than 1920×1080 — 33% more. They differ in shape too: 1920×1080 is 16:9 while 2560×1080 is 21:9, so windows and video fit differently.
Same pixel density, same sharpness — the ultrawide just extends your desktop a third wider. It's the cheapest way into 21:9 multitasking, though at 29 inches it's no sharper than a 23-inch 1080p panel. If you mostly watch 16:9 video, the extra width sits unused as black bars.