the SUB Sterling is what the name implies- the SUB version of the popular Sterling model. the original Sterling model was the subsequent bass by Ernie Ball to turn heads (after the Stingray) due to its sheer tone versatility; it's one of the very few bass models ever to feature a pickup selector. the Sterling differs from the Stingray in design by virtue of its bass-side cutaway, it's more slender there + the tailend body curve is slightly offset unlike the very round Stingray.
unfortunately, the SUB Sterling
does not feature a pickup selector but critics have hailed it to be a slightly better manifestation of the SUB bass, more midrange defined & lighter in mass. like all SUB models of th Music Man series (SUB1 guitars included), these aren't a cheaper version of the original manifestations offererd by the manufacturer, they mimic their predecessors design but sound markedly different simply because of the differences in wood & finishing processes which affect tone.
similarly, if you think that Fender's Highway1 & the SUB are cheapos to help the company sell quantities, then you've missed the point. 8)
how the original Sterling looks like (note the pickup selector):