Worth the money getting the Celestron version. The reducer is massive in size and is perfectly matched to the Edge 11 optics. You may find it hard finding anyone contemplating giving their reducer up unless they are selling all their gear or switching over to planetary.
Your other alternative is the Optec Lepus HD Telecompresor. It is considerably cheaper but is more fiddly as it uses specific camera mounts and gives 100mm back focus compared to 105mm for Celestron reducer.
Greg
Thanks for the advice Greg, yep am only interested in the Celestron reducer and I had the same suspicion about finding one second hand! Long shot me thinks.