What are some of the best uses for the Quadra?
With its low cost, enclosed design, and familiar UI, the Quadra can be used almost anywhere where video isn't the primary application.
It makes a great computer for learning to program, at home or in a school lab. Or as a home server (for example, ad-blocker). Or as a remote access endpoint for viewing security cameras anywhere in the world.
As a largely Raspberry Pi compatible Linux open-source computer, you are limited only by your imagination.
When is the Pi 4 a better option than the Quadra?
There are primarily two areas a Raspberry Pi 4 is a better option than a Quadra:
1. The Pi has a 40-pin header for connecting to external devices. The Quadra does not, so the only easy way to connect to external devices is via its USB ports. But for this purpose, a Raspberry PI Pico W ($6) is probably a better and much less expensive option.
2. The Quadra is roughly equivalent to a Raspberry Pi 3. The Raspberry Pi 4 has A72 cores vs A53 cores used in the Quadra and Pi 3. This, plus the better GPU/VPU and driver support in the Pi 4, means it plays videos more smoothly and at higher resolution, for example.
A general rule of thumb is to use the Quadra when a Raspberry Pi 4 is overkill or you would like a much less expensive option. Or you want the simplicity of everything just working out of the box without assembling it yourself.