The short version of the story is in the title: I bought a Fleks3D system build plate for my XYZ da Vinci Jr. 1.0w and it turned out to be not compatible. I wasted $50.

A filament 3D printer creates an object in 3D by building it up, layer by layer, from the bottom to the top. That necessitates that the bottom layer sticks well to the build plate. If it doesn't, the movement of the print head moves the object around, and the next layer doesn't go to the right place. Many printers come with glass plates, so you need to modify that build plate in order to make your prints stick. But not too much, because otherwise you can't get them off easily.

There are a lot of homebrew solutions to that. Some people use a glue stick. A less messy method is using masking tape, the sort used when painting your house. But as the masking tape is at best 2" broad, you then need to put 3 rows next to each other without overlapping or leaving gaps, which is a bit fiddly. And you need to replace it after a few runs. XYZ Printing is selling 6" bed tape, which works great, but isn't exactly cheap at $1 per square.

So when I stumbled upon Fleks3D, who are offering a re-usable plastic build plate system, I thought it would be worth a shot. The idea is that the plastic is removable, and can be bent for easier removal of the plastic item printed on it. So I bought the 6"x6" system, which I thought would fit on my XYZ da Vinci Jr. 1.0w build plate. Well, it did fit more or less (surprisingly I found it a bit small, in spite of the print area of my printer supposedly being only 5.9"x5.9"). But what I hadn't considered was the thickness of the added Fleks3D build plate of over 3 mm. The instructions helpfully suggest to lower the bed by slightly more than 3 mm, but on the XYZ printers you can't lower the bed at all. You can raise the print head with the Z-offset setting, but not by much. So even with the Z-offset set to maximum my print head scratched the Fleks3D build plate and couldn't print.

Now I could have tried to remove the glass plate to get a lower surface. But the surface below the glass didn't look very flat, and the removal not easy. I was worried that if I messed that up, I would have no working build plate at all. Furthermore experimenting with the Fleks3D plastic surface showed that it wasn't as flexible as I would have thought. And I could see that after some bending it wouldn't necessary be level on the build plate any more. So I decided to cut my losses and just gave up on that system. I got some more XYZ bed tape, and when that runs out, I might try the much thinner BuildTak system.

[EDIT: Actually it appears as if the nozzle scratching over the Fleks3D build plate has damaged my nozzle. I need to buy a new nozzle system. :( ]