No idea what Open Metal organ stop sounds like 😅.... or many of the others!
Organ playing does seem to be a feat of multiple coordination way beyond me - I'm not even all that keen on the noise it makes! I just sing 😄
Metal (usually a mixture of tin and lead) as opposed to wood, open (at the top) pipes are half-wavelength long. Closed (or stopped) pipes are closed at the top with a stopper and are quarter-wavelength long, thus sounding an octave lower than an open pipe of the same length. Stopped pipes have a different overtone series than open ones, because they only produce odd harmonics. This affects the sound. Stopped pipes take up less space for the same basic pitch. Trust me, playing the organ is a lot easier than explaining all this clearly!