When comparing Planets vs Calendar, the Slant community recommends Planets for most people. In the question“What are the best custom Android Wear watch faces?” Planets is ranked 1st while Calendar is ranked 20th.
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Pros
Pro Two themes to choose from
Pro Displays the actual current positions of the planets
The watchface collects NASA data and uses it to put planets in their appropriate places.
Pro GNOME native integration
Pro Currently in active development
GNOME Calendar is improved with every release cycle of GNOME.
Pro Simplicity
Calendar for GNOME aims to find the perfect balance between features and usability.
Pro Synchronisation
It has online accounts integration.
Cons
Con Initial spin makes it hard tell time with a quick glance
Each time checking the watch all the planets spin wildly before settling into position. It can be distracting and arguably unnecessary.
Con Eats up battery life
Eats the battery at about 3 times the rate of the standard watch face.
Con Cannot print
Con Extremely buggy
Con Poor interoperability with online calendars
Does not connect to Fastmail.
Con Far too simple
Con FAR too tied into the GNOME infrastructure
The UI and configuration presume you are running GNOME, and has the ugliness of a GNOME application. Configuration, as is usual for any GNOME application, is pretty much nonesistent.
Con Can't read 'all-day' events with dark theme
Text is white on light blue with dark themes. The workaround: assign all-day events to just one hour.
Con Can't import ics files
Con Continues to pop-up reminders that are turned off and they cannot ever be removed
The GNOME Calendar displays pop-ups from an old Google Calendar that was used. That Google Calendar has long since been removed from GNOME, and even with the notifications turned off on the GNOME Calendar, the pop-ups still happen.
Con Incorrect appointment times when importing .ics calendars
Con No support yet for WebCal
No support yet for WebCal, such as those offered by Facebook events.
A workaround exists. Since this application uses the same background services as Evolution, installing it and adding the WebCal calendars there, also adds them to GNOME Calendar.