One of my favorite tools for leaving effective feedback for students is Kaizena. Kaizena allows you to easily leave audio and text feedback for students in a Google Doc. This is a free service and one that I suggest to a lot of people because we should be more focused on feedback than grades in order to help students learn. Also, audio can sometimes be more powerful than text alone as we say a lot in how we say something and we can articulate something more easily while speaking sometimes. I also find that it is a lot quicker to leave audio feedback than text feedback if I want to ensure I get my point across.
The update to Kaizena does change how you leave the feedback but the workflow seems to be better than before. While looking over the tutorial videos in their post, http://ift.tt/1KurjYj, you can easily see how you can track your comments over a longer period of time than just one document.
You install the shortcut using the Add-ons in a Google Doc, which means you will have to make sure your students install that Add-on also into their Google Docs. The limited amount of time it would take to help your students install the Add-on and learn how to use it will be made up for by the growth that they can make when you are giving more effective feedback.
If you are looking at improving the feedback you give to students, give Kaizena a try. If we want students to learn and continue to learn, we must focus on the feedback we give and how it affects them as a learner. Giving effective feedback is a great way to instill a growth mindset into our students where just only giving grades is a way we will ensure a fixed mindset and limited learning.