Stream Line is a lubricant only. Lubricating a line is awesome because it improves casting distance and accuracy. Fishing guides have been known to leave a bottle in their boat to give their clients any advantage that they can.
Scandinavian Fly Line Cleaner lubricates a line, but also improves floatation. This means that it improves presentation, makes mending easier/more effective, and provides an overall better fishing experience.
Line Speed does all of the above but also conditions a line and provides a UV protection. This means that not only will you maximize your line’s performance, but you’ll also make sure that line lasts.