I've taught both SDI SOLO and PADI Self-Reliant. The courses are almost identical. The biggest differences are the training materials -- SDI has some, PADI does not -- and the number of required OW dives: 2 for SDI, 3 for PADI. The SDI standards also allow a SpareAir as a redundant air supply, which is ludicrous, and I don't know any SDI instructors that allow that. Some dive operators will not accept the Self-Reliant card because they think it does not mean solo. They are wrong, but it is their dive operation. I used to teach the class using the SDI materials and the PADI standards, and give the student both cards. You are correct, the course value is mainly up to the instructor.