My compliments for the desire to try out alternatives, and not stick to 'out of the box' -- that's the FOSS attitude!
Unless you have concurrent users running different desktops at the same time, the other desktop environments will not slow down the system. They are mainly sitting statically on the disk.
In fact, you are likely to find out that some lightweight desktop environments will provide a snappier user experience overall, notably on lower end machines. If you particularly like one, you could even consider replacing the ubuntu-desktop package by the desktop environment of your choice.
If you want blazingly fast (and completely austere), try running only X with a window manager. Ah, the good old days ...
TL;DR - yes, these Zoom and Night Light are only for GNOME.
As far as I can see from htop and other clues as
# find Zoom
$ grep -r Zoom /usr/share/applications/
/usr/share/applications/gnome-universal-access-panel.desktop:Keywords=Keyboard;Mouse;a11y;Accessibility;Contrast;Zoom;Screen;Reader;text;font;size;AccessX;Sticky;Keys;Slow;Bounce;Mouse;Double;click;Delay;Assist;Repeat;Blink;
/usr/share/applications/gnome-keyboard-panel.desktop:Keywords=Shortcut;Workspace;Window;Resize;Zoom;Contrast;Input;Source;Lock;Volume;
# find Night
$ grep -r Night /usr/share/applications/
/usr/share/applications/gnome-display-panel.desktop:Keywords=Panel;Projector;xrandr;Screen;Resolution;Refresh;Monitor;Night;Light;Blue;redshift;color;sunset;sunrise;
Their Exec fields are the following:
# Zoom
$ cat /usr/share/applications/gnome-universal-access-panel.desktop | grep Exec
Exec=gnome-control-center universal-access
# Night
$ cat /usr/share/applications/gnome-display-panel.desktop | grep Exec
Exec=gnome-control-center display
# Both
$ cat /usr/share/applications/gnome-keyboard-panel.desktop | grep Exec
Exec=gnome-control-center keyboard
They are shown only in:
# Zoom
$ cat /usr/share/applications/gnome-universal-access-panel.desktop | grep Show
OnlyShowIn=GNOME;Unity;
# Night
$ cat /usr/share/applications/gnome-display-panel.desktop | grep Show
OnlyShowIn=GNOME;Unity;
# Both
$ cat /usr/share/applications/gnome-keyboard-panel.desktop | grep Show
OnlyShowIn=GNOME;Unity;
above means only GNOME and Unity.
The top icon toggles GNOME specific configuation keys - for example Zoom toggles
/org/gnome/desktop/a11y/applications/screen-magnifier-enabled
between true and false. And this setting is expected to be applicable only to GNOME.
And Night Light toggles the GNOME-only configuration key:
/org/gnome/settings-daemon/plugins/color/night-light-enabled
So we can see that these Zoom and Night Light are related only to GNOME and Unity desktops.
Other desktop may have (or have not) alternatives for them. Night Light may be replaced with RedShift, accessibility tools are usually presented in desktops (for example MATE has mate-at-properties).
Best Answer
I have unity, gnome 3, cinnamon, xfce, lxde, kde4 installed and have no problems. Just don't run distribution setups like
xubuntu kubuntu-full, etcYou might run into a problem on a low resolution monitor which is lightdm the one unity uses won't be able to display all at once. If that happens run the following
sudo dpkg-reconfigure lightdmand switch it to gdm, kde, or something besides lightdm.I find cinammon the best, especially if your coming from windows. And it looks beautiful and simpler than kde. xfce4 is 2ed choice and I would reccomend if you have a low end system. Forget about unity, gnome3 to introduce to linux. Also tell your friend to check out this video before trying cinnamon or to watch any of her videos for desktop environments or distributions to try. Mom tries it and loves it, was also her favourite OS after her son got her into linux in this video.