It works like a micro SD card with better read/write performance (especially on 4k read/write) and have longer lifetime. RasPiKey has Raspbian (Raspberry Pi OS) preinstalled and allows you configure SSH login and Wi-Fi connection before booting your Raspberry Pi. As a result, you can use your Raspberry Pi without display, keyboard and mouse, and access your Raspberry Pi via SSH session.
RasPiKey is a “plug and play” accessory to most Raspberry Pi models. If you have Raspberry Pi 4B from rather old batch, which has rather old firmware that could not recognize RasPiKey, you may need to update the bootloader of your Raspberry Pi 4B beforehand (please find more details in the user manual).
RasPiKey has two varieties: the 16GB RasPiKey comes with a black lanyard, while the 32GB RasPiKey comes with a blue one.
32mm x 19mm x 1.6mm
16GB: Samsung KLMAG1JETD-B041 (datasheet)
32GB: Samsung KLMBG2JETD-B041 (datasheet)
0~80%RH, no condensing
RasPiKey has much better read/write performance than all SD cards on Raspberry Pi 3 and 3B+. Below is the benchmarks (using the same method here) on Raspberry Pi 3B+:
By upgrading the firmware on Raspberry Pi 4B, DDR52 mode will be supported and RasPiKey can have much better performance now (please find details in the user manual). Below are new benchmarks for RasPiKey on Raspberry Pi 4B (with DDR52 mode supported).
You can find the user manual here: http://www.uugear.com/doc/RasPiKey_UserManual.pdf