Hetty - When I got rid of the granite from the kitchen I thought it would be ideal for the top of my potting table. Wrong! It looks great and it's nice when the temperature is moderate or it would be good in shade...but the sun heats up the granite (as it would the stainless steel) that it makes it unusable for hours at a time.
An umbrella is useful and does help but it manages to be in the wrong spot all the time and has to be moved to avoid the sun.