I uploaded the .mp4 file from this video: vimeo.com/5792065 to their site(betterencoding.com). They turned my 180mb file into a 23mb .mp4 file.
I'm not sure, I can see a difference - can you?
With a weekly max. of 5GB of Vimeo space, I'm not going to use their service for my short videos but since each Vimeo file needs to be below 1GB,
longer videos might benefit from this
If you can run both together and mute the sound on one file you can make a direct comparison