Ken Curtis gained some fame as a big band singer before joining the Sons of the Pioneers. A great singer who never really lost the aw shucks voice. Festus Hagen was closer to his real speaking voice than most people imagined. The only complaint I ever had of TSOTP was in the movie Rio Grande when they were the Regimental Singers. Curtis sang I'll Take You Home Again Kathleen beautifully but with big D Martin guitars in a movie set before (1874)Tom Westendorf wrote the song(1875).
And it wasn't their fault anyway, no one would argue with John Ford.

The Sons were my favorite western band for a long time. Even when the lost the Farr brothers they still had better voices and instruments than most western bands.

I truly believe they were as much a jazz swing band as anything else.
Listen to Cajun Stomp or Kilocycle Stop and you will swear it is Stefan Grappelli and Django Reinhardt you are hearing.

Don