You are right, the information on the website is somewhat confusing.
Essentially there is an "evaluation mode" and a "trial key", which turns off evaluation mode for the duration of the license (~ 1 month).
So, if you install SpecFlow+ Runner without a license key of any type, it runs in evaluation mode. When doing so, all of SpecFlow+ Runner's features are available. However, an additional test is added that introduces a delay each time you execute your tests. But functionally there are no restrictions - which is what the information on the website is trying to convey.
The trial key simply removes this delay when executing tests. Once the trial key expires, SpecFlow+ reverts to evaluation mode.
Note that the license does not permit you to use SpecFlow+ Runner in evaluation mode for production purposes.
Does that make it clearer? :)