Advantages I see:
- you can hop on and off wherever you want. That makes them useful for short trips
- no waiting time; you can hop on whenever you want. That likely makes up for lack of speed on short trips.
- if built at ground level, pedestrians can cross the line fairly easily wherever they want (hop on, hop off on the other side), so these wouldn’t split cities in half the way railways do, but only for pedestrians.
Disadvantages I see:
- slow for longer journeys
- power inefficient if there are few passengers (trains are, too, but this is a really, really long train. Imagine moving these 3km of track to move 10 persons). You can’t scale down capacity for less busy hours.
- all maintenance requires shutting down the system (in contrast, with trains, you take off the train and put another one on for most maintenance)
- ¿safety?