I myself answered a question on the so-called "Shabar Mantras" here.

This webpage claims that these mantras are auto energized or Siddha so to speak.

A shabar mantra is quite different from a classical or Vedic mantra. One needs to attain siddhi to use a Vedic mantra but it is nothing like this in case of a shabar mantra. Shabar mantras as auto-energized and can be used even by a common man easily to bring his wishes true.

Is that true?

Also does that imply that for these mantras upadesha from Guru(initiation) is not needed?