When comparing Orion vs Papirus, the Slant community recommends Papirus for most people. In the question“What are the best gtk3 themes?” Papirus is ranked 3rd while Orion is ranked 29th. The most important reason people chose Papirus is:
All icons look pleasing, especially with the Arc theme.
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Pros
Pro Plug-ins including Pixlr image editor
Pro Built for front-end development
Orion was developed specifically for front-end development, making it a strong option for front-end developers thanks to features like syntax validation with ESLint and HTML content assist.
Pro Eclipse-like UI
Orion is developed by Eclipse and shares a lot in common with the Eclipse IDE UI.
Pro Sharp, flat, and fresh
All icons look pleasing, especially with the Arc theme.
Pro Familiar
Used on Lubuntu and BunsenLabs, for example.
Pro Active development
Cons
Con No runtime environment
Does mostly do file editing, but without good project support, web terminal, build/runtime environment.
Con JavaScript only
Orion currently only supports JavaScript.
Con Under GNU GPL3
This limits the use elsewhere.
Con Contrast issues / No border around icons
It makes the the fast and makes it simple to add more icons(since you can simply scale them) however the contrast is lost in some situations.
Con No Ideas
It just copies the icon-syle from a different system.
Con Just another material style copy
Con Lacks icon for backintime
Backintime tray icon doesn't display on the panel because Papirus lacks the icon.