> 2- Isn't it better to use a login manager that is 1- graphical and 2- uses the same GUI tech as your DE

A text only login manager could spare some more resources on small systems, since once the desktop environment has been loaded it keeps running anyway. I use LightDM and XFCE for example, and if I look at LightDM memory consumption, the amount although not huge is neither trivial; I guess small embedded devices would benefit from this.

  $ sudo pmap `pidof lightdm`

  2021:   lightdm --session-child 14 23
  000055728c276000     28K r---- lightdm
  000055728c27d000    168K r-x-- lightdm
  000055728c2a7000     76K r---- lightdm
  ....
  ....
   total           163696K
  1795:   /usr/sbin/lightdm
  0000555cca10b000     28K r---- lightdm
  0000555cca112000    168K r-x-- lightdm
  0000555cca13c000     76K r---- lightdm
  ....
  ....
   total           236188K