

Ender 3 Pro is a completely offline printer. It has a microSD slot and a USB port, that’s it. No network connectivoty at all. It runs Marlin firmware which is a long-standing Arduino-based open source 3D printer firmware. It’s highly customizable and upgradable. I added a CR Touch bed probe to mine and rebuilt the firmware to enable the unified bed leveling features. It’s not the most user friendly but it’s a decent, cheap platform, fully open source, and puts out decent prints.

I don’t know much about the Snapmaker U1 other than what’s stated on this thread and on their site. Just looks like a more open alternative to Bambu if you need fancy features like multi filament printing.
I buy most of my filament from Micro Center (their Inland brand) and some I’ve gotten from Amazon.