The MF-5021 is a 21" version of the MF-5017 (17") which are capable of displaying screenmodes between 15 and 38Khz, hence they can display the Amiga's native screen modes. They are probably quite rare as they are fairly expensive and were only sold for a short period of time, also graphics cards were in common use when they were released so many people probably preferred a monitor with higher scan rates.

Thanks to Ralph Ewers