There is also another physically-identical keyboard, the Thinkpad Multi-Connect Keyboard, which allows you to toggle between 3 paired devices.
It appears to be China-only, and only available through sites like AliExpress. There are no drivers for any OS (iOS/Android or Windows), just a single-sheet manual is available here: http://webdoc.lenovo.com.cn/lenovowsi/new_cskb/att/147372/%E5%BF%AB%E9%80%9F%E4%BD%BF%E7%94%A8%E6%8C%87%E5%8D%97.pdf
Unlike the Compact keyboards, the keyboard does not have (known) built-in
Fn-Lock functions, Fn, Fn-F1 and F1 are all separate scancodes, so they can be
remapped using a hwdb database.