I'm afraid I can't comment from experience - crew rest on the long haul flights I operate is usually 20 mins (if we work very fast!) on an atlas box in the galley (yes charter!). My preference would be for a bunk (I would find it difficult to sleep or get very comfortable in a seat) in an area not readily accessible from the cabin - I dont think that a curtain provides an adequate barrier from noise or interruption - a small minority of pax will attempt to open the curtain. I have experienced this both with galley curtains, and when screening a toilet off for use by a disabled pax. IMHO if crew rest inflight is an option then it should be made as comfortable as possible.