They are very popular. Cathay Photo, Tk Foto, Oriental Photo and other are selling them but the older version only allow EF lens not EF S made sure you get a newer version that allow to be use on both EF and EF S
I own the Kenko Extension tubes set of three for Canon, not so easy to handle for macro photographic and later I bought a EF 100mm f/2.8 macro. The macro lens is more easy to focus and very sharp.
I own the Kenko Extension tubes set of three for Canon, not so easy to handle for macro photographic and later I bought a EF 100mm f/2.8 macro. The macro lens is more easy to focus and very sharp.