When comparing Orion vs Materia, the Slant community recommends Materia for most people. In the question“What are the best gtk3 themes?” Materia is ranked 6th while Orion is ranked 29th. The most important reason people chose Materia is:
Includes support for Gnome Shell, has a Cinnamon desktop theme, plus supports XFCE, Mate and all the usual suspects.
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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 Good support for various DEs
Includes support for Gnome Shell, has a Cinnamon desktop theme, plus supports XFCE, Mate and all the usual suspects.
Pro Under continuous active development
Responsive and helpful developer.
Pro Customizable via Oomox app
Users can build completely personal version easily using Oomox Gui app.
Pro Corresponding theme for Qt/KDE
There is a corresponding theme for the kvantum-engine under Qt/KDE.
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 No Round Corners
Let's be honest Round Corners is a must addition in 2022.