I've never heard of "reactive testing" so I'm not sure what exactly that means. Any idea?
A blended strategy in the sense of using different test techniques and approaches can be a powerful idea but you (and your fellow testers) need to understand when to use them and when not to. Always make the strategic decision based on the context of your test project and your testing mission. For some projects it might make sense to do automation while on others it won't.
Now to answer your questions:
So I was about to implement in our project but now I realized - how
can our testers verify the requirements?
Ask yourself what is your testing objective, what is your mission? Do you need to verify requirements, or rather help identify regression issues? This will help you determine your techniques. This might change with each project. Context is key, remember there are no best practices just good practices in context.
None of these strategies really uses functional specifition (or e.g.
stories and their description), unlike classical requirements-based
one, which authors mention to have issues with agile approach because
Are you saying you've never heard of someone automating requirements testing or automating functional testing? Whenever I use a risk based approach to testing I look for all available information including specs. I don't understand your logic here.
That makes sense, however, it means testers cannot really verify the
functionality. Do I get that right or is there something I cannot see?
I think you missed something here. Remember techniques overlap as do approaches. You can test functionality while automating it.
So far on all projects I have been to, testers in the beginning of the
sprint wrote test cases in advance, which does not go with these
Now you're talking about a scripted approach to testing as opposed to a more exploratory one. You can use either approach with the techniques listed (note I don't know what book your referring to so I'm only responding to what you've said).