Sorry for slipping through the cracks.
Our displays predominately have many common features. Commands like clear screen work on every display we have.
The first major difference will be the graphics vs alphanumeric. Obviously draw line doesn't work on an A/N display, and custom characters are not supported by graphic displays.
VFD vs LCD will introduce another difference. Brightness on a VFD vs backlight brightness and contrast on an LCD.
In the A/N displays, 4 line displays support medium and large digits, while 2 line displays only support medium digits.
Then the size of the keypad and number of GPOs will be another factor.
In spite of all of this, our displays are quite consistent, and should have large amount of overlap. Really, I'd grab a display that scratches your itch first, then when you put in the next display you'll have a lot of "Oh, I already have that command" moments.
If you do run into problems, just let us know. We're usually a little quicker getting back to people on the forums.