This thing was designed to prevent the chain from dropping out of the chainring on bicycles with one by 1x drivetrains and a E-Type low direct mount frame.
There are three files for three different chainring sizes: 32T, 34T and 36T.
This thing is a mechanical part, as such, strength is required.
PLA is good enough, but you can expect better durability from PETG or ABS.
For better layer adhesion, chose a higher end of the recommended printing temperatures for the filament you use, avoid layer heights lower than 0.2 mm and set a line width of at least 0.5 mm.
Walls, top and bottom thicknesses of around 1.5 mm with 20% infill work great.