I currently have a XYZ Davinci Jr 3D printer and it prints just fine - I have used the printer for a number of my "arduino projects".
The only issue with it is that it is sold to only use proprietry filament and this is over double the price of other filaments - so does get expensive
This is down to the way that the printer has been designed as each filament roll comes with its own RFID tag.
This tag holds a NTAG213 chip and on it is stored the filament length and more importantly the filament remaining.
Some clever people worked out a way to get the password that the printer supplied to the tag to unlock it for use.
We can now edit the data on these tags to "refill" them - this can be done with Arduino solutions or NFC enabled Android phones.
I came across the EMUTAG whilst searching for writable NTAG chips and it was the only thing I could find that has a re-writable UID.
Using the card no, password and PACK code from my own XYZ NTAG cards, I could use the EMUTAG in my printer instead of using the supplied card.
As I hadn't updated my firmware on my printer, the printer also had no problems with me "refilling it" - i.e setting the card data so it reads as full again.
Unfortunately it looks like XYZ were on the ball and changed later versions of the firmware (post 2.2.4) so as not allow refilled cards - they just show up as "unregognised" and won't allow printing.
They also stopped users rolling back the firmware versions after 2.2.7.
The firmwares for the Mini and Jr Wireless printers have also been restricted this way.
To this end, myself an another have devised a solution using the EMUTAG and previously obtained Card UID, passwords and PACK codes so that owners of these printers can use an EMUTAG and their own non XYZ filament to print with.
All this info is available in the SOLIFORUM community forum
Using an Anruino Nano and a PN532 RFID card, we have a hardware and software soltion to make the job of wrtiting to the EMUTAG easy.
The .Net applicaion can be used to write the required data to the EMUTAG to allow it to print.
The software also allows saving of the card's data so that all isn't lost when changing batteries.
We can be contacted on that forum.