I have found many such flexagons, but they are either difficult to print or need some kind of reworking or gluing. So I made up my own version. All parts of my version are easy to print without support, and no cutting of integrated support is required. I divided the body into two parts, they are assembled with a snap in connector, usually no gluing is required. The hinges are also snapped in, no additional filament is required as an axis. In my opinion it is so much easier to print and assemble. Additionally you can print the body in two different colors, if you like.

I have added a version which prints as one part complete.

Print instructions

You need:
12 pieces of body (or 6 pieces of the body_complete),
6 pieces of connector (to connect the half bodies),
12 pieces of hinge

I recommend to first print the bodies, and afterwards to print one connector to test the clearance. If the connector is too tight, you can print the scaled version (98%), or scale with your slicer in X/Y to your needs.
Instead you can also print the single part one, without to have to connecting parts.

Do not print the hinges together with the rest, because such small parts can get loos from print bed easy.

Post-Printing

To assemble the hinges, you probably need needle-nosed pliers. First mount all hinges, then the body parts.