This episode is generally regarded as one of the worst of the series. Dr Smith swaps places with his doppelganger, gunslinger Zeno, who clearly has different attitudes and voice intonation to Smith but yet the Robinsons can't put two and two together. He also makes a pass at Judy which is highly out of character.
Clocking in at 51:51 minutes, this is the longest episode in the series' run.
The writer of this episode, Michael Fessier, wrote the screenplays to the Fred Astaire musicals You Were Never Lovelier (1942) and You'll Never Get Rich (1941).
This is the second time Dr Smith has had a duplicate. The same thing occurred in the Season 1 episode His Majesty Smith (1966).