350 is not a curved panel like the other 3.
591 is white, same stand as 396. Could be as simple as varied naming for different markets (power connector types, materials restrictions, etc.). They all use the same 1800R VA 1080p panel.
What will you be using the monitor for? If gaming, any reason you wouldn't want something like a VG248QE, XL2411, or XB240H for about the same amount of cash?