Sorry for posting 6 years later, but I have exactly the same keyboard.

I will say that it's possible to take control of some wireless keyboards (even with AES encryption) and install keylogger (including this one). There is evidence that it's possible: https://www.theatlantic.com/technology/archive/2016/07/hackers-can-spy-on-wireless-keyboards-from-hundreds-of-feet-away/492962/

Also, you can't be sure that there are no backdoors here. Some manufacturers and governments have been known to put backdoors inside their encryption solutions.

Your best bet is to use a wired/laptop keyboard if you need to type your password.