This method of using the rest (or the mechanical bridge over here) has been around a long time. I first saw that technique about 40 years ago. It was the subject of a recent discussion somewhere in the pool forums. Some think it is not a standard, allowed use of the bridge but I think it's OK especially since most pool tables do not have a full complement of support equipment. In fact most pool tables only have a cheap cast metal bridge head that will put horrible scratches and dings in your shaft if you are not very careful.
Here is a description in a 2001 article in Billiards Digest (see the second column of text):
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