Conversation so far:
How did Namdev start his teachings?
What were the Bhajans and its connection to Namdev?
Namdev composed bhajans, that is songs meant to be sung to music. A Bhajan literally means a thing enjoyed or shared.
Who did Namdev teach bhajans to?
Did Namdev have help composing the bhajans?
Are there any other interesting aspects about Namdev and Bhajans besides its composition?
The musical genre of Namdev's literary works was a form of Prabandha – itself a very large and rich genre that includes dhrupad, thumri, tappa, geet, bhajan and other species.
Were there any people who opposed Namdev and his teachings?
When was Namdev's Bhajans created?

Question: were the Bhajans useful?
Self-contained rewrite: Were Namdev's Bhajans useful?