Designed to hold the stock spatula, two other spatulas, a standard sized vial of nozzle needs, and the 5 types of hex keys for an Ender 3.
Designed to be printed with the top face as the bottom layer (rotate it upsidedown to print). Internal supports are likely needed on the pieces that slot into the rail. Should be a snug fit, but if you're having trouble sliding it on, a quick hit with a heat gun should help.
The author hasn't provided the model origin yet.