I was already sleeping on a foam topped mattress and having great results made me wonder about adding a couple inches for even better results.  This is the best night's sleep that I think I have ever had!!   I am happy when it's bed time - as I know I'm heading in that direction I feel a smile n my face.  THere is a nice cool night's sleep waiting for me that I cradle into fast asleep within minutes.
The added foam topper does not tend to slip or move around at all - I sleep with a ton of movement.  My sheets fit just perfectly and the added depth made little difference in that.