AFAIK, the Super Speed model was never an adjustable. There were a few variations on the adjustable that looked somewhat similar, the Slim, the Fatboy, etc.
What adjusts is the amount of gap between the blade and the guard. The larger the gap, the more exposure the blade edge has, the more aggressive the shave. Set to "1", the typical Gillette is so mild it will hardly shave anything. Set to "9", it's a pretty decent shaver, but a light touch is needed to avoid irritation or worse. As I understand, Merkur adjustables have a wider range and are more aggressive at the high end.
How important is this feature? Let's just say this: I have a couple Slim adjustables and a Fatboy. I rarely use them. Some guys like to shave one pass in one setting, change, and do another pass or different direction at a different setting. That strikes me as OCD, but YMMV.