Is this a good setup to run 2+ bitcoin instances?

Each one is running under a separate user, so no need to set -datadir.

bitcoind -rpcport=8721 # this will be the master running as root
bitcoind -rpcport=8121 -connect=127.0.0.1 -nolisten  # slave 1
bitcoind -rpcport=8216 -connect=127.0.0.1 -nolisten  # slave 2

The above is for 2 users. They connect through the master node.

Am I missing anything?