I think he was using MX Linux(Debian+Xfce) and installed MATE on top of it... which I think is a bad idea, mixing DEs is usually messy.
Some points of the long review:
Desktop icons
The one thing MATE did not let me do is - make the desktop icons disappear. Here, I did need to use dconf-editor and make a "tricky" configuration change. Some distributions, like Linux Mint, do have helper tools that work around these, but the stock environment needs some polish.
Menus
MATE does offer its own search-enabled menu called Brisk, and it looks reasonable. However, Whisker in Xfce is superior, and it can also be resized. Brisk did not have an option to change its height and width, resulting in partially cropped menu entries. That just looks odd.
I've suggested this already on the Thoughts & Feedback section, if not enabled by default it could be an option somewhere inside Mate Tweak, some people like to resize the menu.
System tray icons
Going up to 36px or alike makes icons pop up in size in a rather unpredictable manner.
I think Martin said the other day that you guys are working to improve this area of the panel.
Screensaver
As it turns out, there's a screensaver. And it would not let me type when I tried to unlock the screen. I had to open a virtual console and kill the program.