I've got a Prusa MK3 at work that we've been using a bit recently. We bought it unassembled, I assembled myself, that took a fair amount of time. I wouldn't necessarily go that route, it's neat to see how it works, but there's a lot of ways to mess things up if you lack attention to detail.
Powered up and started printing immediately, so it at least I can read the instructions.
I'm a machinist and use CAD and/or CAM software everyday for the last decade, so the learning curve was pretty easy for me. The Prusa slicer software is free and very solid. The claim to fame of open source is really great. Users provide feedback and they seem to listen. If you have a question, just google it, I'm sure the answer is already out there.
We pre-ordered their new XL printer because we could use the larger working envelope.
I've only printed PLA filament for prototyping purposes, Prusa factory setting were spot on and haven't really needed to tune anything from stock.