so things are stored on the key itself?
Yes, in a way that one-time password secrets and private keys can't be
exported out of the device for security reasons.
We recommend to use one-time passwords which are more secure than
ordinary static passwords. However, for legacy reasons you can store up
to 16 static passwords on the Nitrokey. Of course you are free to store
multiple passwords for a single site.
Said for you, we aim for high security solutions instead of these questionable
web services...