I was using casio fx 82 while education. It hadn't function recall (recent calculations you made) but new ones had this option. Also I used it to remember complex equations while exam, yea I cheated (you can save your equations in the memory of calculator).

- Using alfa (pink letter) keys and memorize your mid-calculations is great. It was like [a(a-b)-b(a+b)] and each a and b having lots of calculations in it. after you calculated and assigned those results to "a" and "b" alpha keys, then point them (simply pointer logic).
- Regression is nice option. you gave couple of points in calculator and asking it next result. ie: (1, 15) (2, 27) (3, 32) (4, 34) and then you can ask what is value for 5.
- Its nice option to recalling recent calculations you made, you may consider this.
- Dot matrix screen and at least 2 lines.

Btw my calculator was cheap, but it was recent. There were expensive casio's exist (fx 5500, fx 6600) but those were old and didn't have these functions. So don't use price as for comparing.