The Canon tubes are way over priced, they have stronger clips etc but when your mounting a 50 f/1.8 on the end that weighs nothing its no biggy, at the end of the day its just air inside.
The Kenko or Jessops ef-s tubes are fine and much better value per mm but fiddly, working distance is poor and a flash unit becomes very important IMO.
50 f/1.8 + 1.4TC + 65mm tubes