The Sounds Good Project
The "Sounds Good" project was a JISC-funded project at Leeds Metropolitan University from 2008-2009. While technology has moved on since then, the project did provide some interesting and useful insights on the use of audio as a feedback medium for students from foundation courses up to Ph.D candidates. I think some of the findings are reasonably extensible to sixth-formers and possibly further down in secondary, as well. Overall, the project found that some initial time investment was required by staff, but in the long run audio feedback was able to save some staff time, depending upon factors like their writing and typing speeds and general technological comfort level. Feedback from students was largely qualitative, but overwhelmingly positive.
Advances in technology have helped as well -- the project mentions issues of file size and sound quality that are rendered moot by our unlimited Google Drive storage and fast internet connection. Methods of sharing with students have improved with the use of Drive and Classroom, as well. Finally, as discussed in my previous post, modern screencasting tools like Explain Everything allow us to combine written and audio feedback into one file, giving students the best of both. (Sounds Good was conducted using handheld audio-only voice recorders, as it predated most tablet computers and smart phones. For a modern take on that same approach, try Voice Memos for iOS.)