Shipping a Nitrokey to Asia - "Goods Mail International" shipping method?

Unlike YubiKeys which I was able to order via Amazon US from Yubico with free shipping, Nitrokeys are not available via Amazon.

When trying to order from the Nitrokey shop, the DHL and UPS options increase the cost of the order by 60% to 90%, with DHL even taking 3 weeks. I will only order one key for now, as I still need to test hardware and software compatibility and compare it to the equivalent YubiKey.

The only cost effective option is called “Goods Mail International”, which is not explained anywhere. Has anyone tried this option? How exactly is it shipped (Deutsche Post, letter/small parcel, air, sea, SAL)? Does it have insurance or tracking? How many days to reach Asia? Does it actually arrive?

The FAQ does not mention anything about this shipping method:
https://www.nitrokey.com/faq

If you want more information, please ask at shop@nitrokey.com