Hey I'm new but i noticed everyone here conciders the ST90 series a starter sax but I do not agree. I own a ST90 alto (my first horn) and a tenor. I want to know what anyone eles thinks about this saxophone.
The ST-90 IV (the current horn) is a horn built by a Taiwanese company -- possibly by several different Taiwanese companies, actually. This isn't a big secret: the horn is stamped "Made in ROC" (brief Google says that it's currently being made by Jupiter, but experience says that there are probably other companies that also do the manufacture).
IIRC, the original ST-90 (no numbers after it) was built by Amati for Keilwerth. This may have continued until the ST-90 III. Keep looking for the ROC stamp ....
None of ST-90's were actually made by Keilwerth.
The ST-90s are all student horns. I've played around with other Amatis and their quality is extremely variable. You can say the same for Taiwanese horns.
As Jim says, if it plays for you, that's great!
I would recommend, however, if you need a major overhaul on it that you consider purchasing a used Yamaha, instead, or if you want an ST-90 brand spankin' new one is only $921 US.