It works fine with a 7D ll. I don’t know about the 5D lll but i’m Guessing it would work. It works on my 6D. I bought mine for snowflake photography. I use it on a mpe 65 macro lens and it works well for that but you should be aware that it produces a rather flat light that allot of macro photographers do not care for. It also produces strange reflections on bugs with shiny shells. I get better results with bugs using a canon twin flash. Yongnuo makes one of these and I hear it works quite well.
7D Mark II 6D 100mm f 2.8 macro 180mm f 3.5 macro, MP-E-65 300mm f 2.8 500mm f4 Tokina 10-17mm fisheye 10-22mm 17-55mm 24-105mm 70-300mm 70-200 f 2.8 Mk II 100-400mm Mk II 1.4 TCIII 2X TCIII 580EX II 430 EX II MT 24 EX Sigma 150-600