For what it's worth, I went through SSI a few years ago and my son just finished PADI. My SSI was associated with a local shop and there was a lot of pressure to buy gear from them, which I did, paying a lot for the previous-years' models of basic gear. My son's instruction was through community education and the only mention of gear was that it be safe and functional. Most of the students rented through a local PADI shop, but the instructor had no financial interest in selling gear.
Our discussions of the lessons seem to show that the curriculum was pretty consistent. SSI seemed to do a better job with the Navy charts and PADI did a slightly better job with emergency situations, but those may be instructor-specific differences. In both of our classes there seemed to be individuals who were so uncomfortable with the water that we wondered why they took the course, sort of a "don't sign up for sky diving if you are not comfortable with jumping out of an airplane"-thing.
Whenever I went into the SSI shop after my certification, someone made a real effort to sell me something...a dive, a trip, a gadget. I quit going in and they have quit contacting me. I get my fills at a PADI shop; the guy who runs it is much more of a soft-sell sort.
My experiences with the first shop have led me to learn to service my own equipment; gathering the tools, parts, and manuals needed for about the cost of one servicing by the LDS. I know there is a risk something the expert at the LDS knows that I don't might cause a problem, but I can tell you that I now know a lot more about my gear than I was taught in class, because the dealer's answer is always "Take it to a certified dealer."