Advice before purchasing XYZ DaVinci Jr.

I have one of the bigger davinci's and have found it quite good, but yes you do tie yourself in with the filament, it can be bought cheaper by getting the refills. once calibrated it does just work out of the box.
I seem to be getting less issues setting it up than a colleague who bought a kit and built it himself.
if you want it as a teaching tool, it doesnt lend itself to teaching how the software is manipulated as it sorts out all of the print settings using the chip in the cartridges.
I have looked at spares availability, and they seem limited with mediocre customer support.
it probably wont just print straight out of the box, the bed will almost certainly need calibration, use the manual method described in these forums, its a lot easier than the inbuilt calibration.
in short depending upon what you want, go into a purchase with your eyes open.
I bought the machine knowing that I would be tied to the XYZ cartridges, would lack the ability to adjust things. I didnt want to get bogged down setting up a machine, my experience is as a CAD draughtsman, so the design work I found easy.
the machine does what I want.

I am in contact with another teacher that uses a Mini in the classroom. We swap ideas back and forth. His Mini seems to be working just fine for them. They are using an EMU tag with it which will help a little with being tied to XYZ filament. They are also using 3Dsimplify and some other designing tools so the students can get a feel for what it is like to design there own stuff. In their case it is not just about the printer, but also about how to design objects to print.

If you go with the JR, you really should consider an EMU tag so you can use non-proprietary filament.

Just another opinion.