My Take
Overall, Kami has high value and is free! You can't beat it. And if you can convince your district to get the paid version - even better. Ultimately, like anything else, it works best the more often students use it.
How I Use It
I frequently assign texts to students to read and annotate. Now that my district is transitioning from paper, to digital copies I found myself struggling to keep up. Many of my texts were in PDF format originally, and I was typing short stories and speeches out word by word. Now that I have Kami, I don't have to do that anymore. I can upload the PDF and my students can take notes directly onto the page.
My students all have chromebooks and so they can type their annotations, or handwrite them using the touchscreen (great for your kinesthetic learners!) They can also highlight in multiple colors which is awesome when talking about different literary elements and stuff. Depending on your settings, once you download the Kami extension, it will automatically open your documents through the app so be mindful if that is not something you are interested in. And similar to other cloud services, it saves my students work automatically. I usually have students take notes and then submit their work using Google Classroom and everything seems to sync fine. (Although I think if you have the paid version the two apps work better together).
I use the free version, so I'm sure the paid version has other features that I can't speak to.
There is a similar extension "Read & Write" that provides translation services and audio pronunciation of words. Based on the description, I thought that I would prefer that, but Kami is definitely my go to app. It's the first thing that I have students download when they get assigned to my class!