I Europe we can choose between Casio, HP and TI. Problem is: Calculators are build for schools, not for using them in real life. Real Calculator: enter Number -> Press sqrt -> read result. Modern gameboy calculator: enter sqrt use cursor to go to number field -> enter number -> press equal -> read result. May be nice to learn how schoolbooks are written, but very inconvinient if you have to use the calculator for real
In the US, we had math books that directly integrated lessons on using the TI calculator (exact function names, button icons, screenshots).
Depends on the models pretty much, I used scientific models like FX 4500P, the 880P, the CFX-9850GB PLUS during my education, and they had programming modes where that isn't the case.