Those are six interesting and attractive cacti Alain, but I want to say "ouch" just looking at them. I've never grown the small South American opuntioides. One of the favorite plants in our C&S society recent show was Tephrocactus geometricus. Neat plants. http://stewart723.blogspot.com/2013/08/plant-show-plants-no-1.html
There are some local growers who are interested in Opuntias and the enthusiasm rubs off. I like the form of some of them but they can be difficult to keep looking nice.The Opuntia parryi in the picture is from a piece which fell off the main plant and rooted in another pot. I tried to repot the main plant which is now in three bits.