I'm editing my previous review.
In short, I love the approach, I love the professional product (compared to say, Doctopus, which will never be adopted by the large majority of teachers) and I love the responsiveness of the company. Even more, as an English teacher, I love the depth of useful feedback I'm able to deliver. A real benefit to students.
However, I discovered that the process of marking essays was WAY too time-consuming. It was frustrating because so much of the time went to endless clicking. I'm absolutely convinced that you can fix this with simple adjustments. For example, if I click to get to a screen with a text box, put the cursor in the text box so I can just start typing. Don't make me move my hands to the mouse, click in the box, then move my hands back to the keyboard. Do that several times per student X 30 students and it adds up. There are multiple examples of things like this that can be fixed. If I could mark papers in 150% of the time it takes me on paper, it might be worth it for the great feedback I can provide. But at 200 or 300% of the time, there's just no way.
I sent you a document with 11 or 12 suggestions, all to do with speeding the process. I'm setting the product aside for now, but I'll be looking for your updates. I know that you are limited by the available APIs. I understand this month's GC update added additional APIs. I hope that helps.