For a removable expansion module, would you recommend a edgeboard connector or a mezzanine board-to-board connector? I'm interested in durability and assembly cost. I came across these edgeboard connectors Are there drawbacks I should know about?

I want to design a PCB for a clock using Arduino Mega, DS1307 RTC module and 1.54” e-ink display module(monochrome). The main board will contain the Arduino Mega, DS13007 RTC module and battery. A small front-panel board will hold the E-ink display. My current prototype does not have any push button but I need to add some of course. I'd like the front-panel board to be removable.

Here is a picture of my current prototype.

 

i would consider making buttons separate, for that i would use 2-pin JST connector - small and cheap.
board can have few buttons and resistors, forming multi-level voltage divider, that is easily read by ADC.

for display i would run cable directly to Arduino. or... put everything on a single shield.

 

For added functionality, mezzanine board-to-board makes more sense BECAUSE it is more compact and takes up less space and it provides greater flexibility. It might also cost less than an edge connector plus the plated PCB fingers. IN ADDITION, most mezanine connectors are cheaper and much more reliable than consumer grade edge connectors.