Having the opportunity, I did some test streaming using Restream.io today.
After configuring the end point settings, which consisted of inputting the end point RTMP URL and Key for each site (i.e., Ustream, Vaughn, etc.), I began streaming to Restream.io, using Wirecast.

It should be noted that stream sent to Restream.io was 196kbps (video and audio in total) and consisted of previously recorded content.

Once the stream was started to Restream.io, it kicked off streams to both UStream and Vaughn, which were the only two CDNs used for testing. The output of each of these streams looked and sounded as expected. This test lasted over an hour and a half.

At some point after an hour and a half the connection from Wirecast to Restream.io was restarted. The reason for this is a mystery, at present. However, it may have to do with the fact that I was streaming from the U.S. to a server located in Europe. Prior to the restart, the output at Ustream and Vaughn looked rock solid. After the video appeared to buffer/pause at both locations, in 10 second sequences.

More testing is required before I could say that I would use Restream.io every week, as, normally, we stream in 2 hour blocks. If I can figure out the mysterious restart, I might jump right on board.

Overall, I would recommend Restream.io as something that one should take a look at if they are wanting to get their stream to multiple end-points, while conserving bandwidth by initiating only 1 stream. More testing on my part, but very promising so far.