If what they did 3 years ago is similar to what you are trying to do today, who cares what they are doing today? (Besides using pg_repack instead of pg_reorg, of course.)
I'm curious because, in the meantime, Instagram could have stopped doing this because 1) it didn't work as intended or 2) they found a better solution.
For what it's worth, we use pg_repack on a regular basis and it works exactly as advertised.