TFA and your blog post both mention SLiM as a login manager, according to the Arch wiki[0]:
"The SliM project has been abandoned (the project homepage is down, leaving a github mirror), and is not fully compatible to systemd, including logind sessions. Consider using a different Display manager or Xinitrc."
Yes officially it is, but notice the date the post was made. It was before the SLiM abandoned :-) I use my self and would recommend LightDM instead of SLiM now. But thank you for pointing this out. I'll post new arch install article one of this days ^_^
I would also like to say that I've been using Arch Linux since 2011 and it works for my development needs. I'm using it with 3-monitors on two separate "GeForce GT 610" video cards. I've tried many other distros including Ubuntu and Fedora both GNOME/KDE. I prefer Arch + XFCE + LightDM my self :-)
"The SliM project has been abandoned (the project homepage is down, leaving a github mirror), and is not fully compatible to systemd, including logind sessions. Consider using a different Display manager or Xinitrc."
Lightdm [1] seems to be a better alternative.
[0] https://wiki.archlinux.org/index.php/SLiM [1] https://wiki.archlinux.org/index.php/LightDM