Screencast-o-matic is a good service for those wishing to create teaching materials or presentations in some form. The advantages as you have seen are length of recording time, editing tools and the fact that you can save your file and publish it in Ping Pong.
However, if you want to test a tool for giving individual feedback to students on work that they have done you might like to try Jing from Techsmith.
Jing is a free programme which you need to download to your computer. You will also need to create an account at Screencast.com before you can use the service the first time. After that you will be able to use the programme to capture a still image from the computer or to create a screencast. When you capture an image you can add text and arrows etc and save it locally or to the cloud service Screencast.com, where you get 5GB storage space for free. With screencasts you can record max 5 min and save it to the same cloud service.
The main benefit of using this service is that you can very quickly capture images or screencasts, upload them to the screencast.com site and send the link to your student, allowing your to record individual feedback for students quickly and painlessly. Please note that you cannot make any edits to items once saved.
For an humourous example of using Jing for giving feedback look at this example:http://www.screencast.com/t/RCzE3za0qw
Russel Stannard from the University of Warwick has used Jing effectively to give feedback to foreign students studying English. In this article Talking Feedback from the Guardian Education one of the advantages mentioned is "Students feel it is more "human" too as they can hear the teacher's voice". Furthermore, it is mentioned that "Students find it engaging and many point out they play the feedback several times".
Watch this video with Russel Stannard talking about video feedback (from Youtube):