These are absolutely fantastic, and open up a whole new realm of possibilities for photography.
As an enthusiastic amateur photographer, I was interested in developing new areas of understanding, and looked in to macro photography. You have three choices - spend a lot of money on a dedicated macro lens, buy some magnification lenses, or buy some extension tubes. After ruling the first out on cost alone, and the second on quality, I was left investigating tubes. Again, you have options - plain, cheap tubes, or tubes with electric contacts. Since the former don't allow operation of different apertures, I looked into electric contact tubes. Canon OEM tubes are about same price for 1 tube, and this gives you three. A no-brainer as far as I was concerned.
The tubes are well constructed. They are instantly recognisable as Canon fit, and fit to camera and lens very easily an intuitively. They store together very conveniently.
Taking very close up pictures with an almost impossibly small depth of field is then simply a question of positioning your camera closer than you have ever been able to do before and hey presto, you've entered the world of macro photography.
I am really pleased that I purchased these for two reasons.
1. you maintain full functionality of the camera. I was a little nervous about this point, as there are older reviews on websites saying these don't work for Canon. These are the up to date version that certainly worked with my Canon 400D.
2. you get three rather for the same money that just one Canon would cost you.