The Mythical HP 17BII++:

Improved by eliminating the MAIN menu, directly assigning menus to the top-row keys (and shifted keys)

And allowing the menu to be turned off (via "EXIT") like the HP42S:

Advantages: No "MAIN" menu means lower-level menu access requires one-to-two fewer keystrokes

Also, being able to turn off the menu allows for two numeric values to optionally be visible

The Mythical HP 35S+:

Allowing soft-key menus on or off like the 42S

Advantages: Reverting to the Pioneer-type soft-key menu system allows up to 6 functions per menu

and reduces menu-function key counts

Also, being able to leave the menu on allows for multiple menu functions to be pressed

without leaving the menu (which further reduces keystroke counts)