How I Use It
I only use this for assessment purposes. It is really easy to assign a running record to students. They record themselves reading, then they summarize what they read (out loud), and finally, they take a quick comprehension quiz. This is a great tool if you do not have the ability to administer running records to all of your students during the day. I also use it as an option for extra reading, though most students do not prefer to use it because the stories are "boring" for them.
In general, RAZ-kids works for me in terms of getting a quick assessment from students. I appreciate that I can get a running record from every student with 5-10 minutes of effort (on their end). It's also nice that I can assign individual students/groups books/stories at their levels. That being said, my students don't love the books that are on this site.