i3wm and MATE make a great duo. The setup is easy and well documented on the interwebz. One issue that I found, but didn't see anybody mention, is that having "Undecorate maximized windows" enabled in MATE Tweak prevents borders being displayed in the tiling mode.
P.S. This option can be also disabled by changing /org/mate/maximus/undecorate in dconf to false.
Have any of you come across this issue as well?