Theoretically 360 terabytes potential storage, so they could theoretically have loaded it up with a bunch of stuff but in reality they have only ever made them ~3 MB in size specifically for these PR pieces.
Without having dived into the specifics, I imagine the hard part is writing the data into the crystal (high detail 3D laser etching?), and the crystal is just a high-purity medium.
if we can make these devices and they can store 360 tb then a high priority for something like nasa should be to put all the digitized books we have currently available in outer space on maybe 100 or 1000 such devices.