I still use an HP 48GX for all my university courses that require a calculator (not many nowadays, the best math courses are the ones without numbers in them). I bought it used in 2020 and it's been one of my favorite sub $25 purchases I've ever made!

HP 48s were forbidden at my school because they could do some symbolic stuff, like derivation etc.

I had one anyway

Could also solve quadratic equations. Also could work with imaginary numbers ( j notation) used in electrical engineering problems

Yep! I had an HP 48 (48SX, I think) in high school. Everyone else had TIs.