It has an ESP32, connectors for the Vindriktning's PM2.5 sensor and fan, as well as an onboard light sensor and more connectors, eg. for I2C. It also replaces the normal LEDs with WS2812's for a customized display (as seen in some of the 3D models mentioned above).
There seem to be a few issues with the USB connector and light sensor, but I haven't yet read through all of the discussions.
It's currently (Aug. '22) only a little over 20€, which seems like a pretty good price to me, considering the parts cost, time it would take to assemble a custom PCB and even the possible issues. Especially since this would be a solution to the overly optimistic color thresholds of the Vindriktning I mentioned in Inspirations/references
For adding more IAQ sensors to my network, I'm now strongly considering building a sensor without Ikea parts, like this one.