My experience stems from experiencing better education. I was going to go through my DM course with my original OW instructor, as I had been with her through all my continuing education all the way through. Still being a rather newer diver, I don't know what I don't know, I didn't know that there was better out there. I did a 2 weekend course. 1 weekend class & pool & the next week end of open water dives. That was the only type of course she taught, I had no idea there was any other type of course. As I later came to find out, I was only taught to the very basic standards. We were only required to perform the skills one time in the pool & 1 time in open water. Was I trained to dive coming out of OW? I would say (with hind sight) marginally. Was I comfortable with my skills? No I was not, but I was told, "you did great!", "your skills are very good". Who am I to question an instructor.
As stated earlier, I was supposed to start a PADI DM course with her in Jan. a few years ago. The course was supposed to start in late Jan./ early Feb. I went to check on the course in early Jan. & to buy books. I was then told that there were a couple of high school students who could not start until school was out in early May. I wasn't happy,... but that is life at times. In late April, I went back to inquire again about the class. This time I was told that the class was being postponed (again) until Sept. when the youngest of the high school students turned 18. This was 9 mos. after the class was supposed to start. How long was I going to have to keep putting my life on hold for the class to start? I found another local shop was going to begin a DM (Dive Con) course soon. I talked with the instructor & was impressed with the information he gave me. I was further impressed when I took a Nitrox from him, as my original OW instructor did not offer Nitrox. Once the course started, I was then introduced to having students repeat skills again & again. I also had my eyes opened that my skills weren't as good as I had been lead to believe.
My current instructor was kind enough to take my under his wing & he worked with me 1 on 1 to get my skills where they belonged & made sure I was comfortable with them. It was a lot of work on his & my part, but he got me there. I learned what quality was, not just the basics. Agency? Instructor? I would say both.
The only negative to SSI is having to be affiliated with a dive shop, though in my case, that's not such a bad thing. The Owner/ head instructor treats us (his staff) very well. We get many perks, are treated with respect as professionals & we are backed up with the resources of the shop. It's a give & take, as is anything dealing with diving. Where you have to give something up, you gain something.