Several commercial breeders use South Devon as the British composition in their commercial Tuli based herds to give the frame size and milk for the continental terminal cross.
This cross is quite popular with Australian breeders, as is the Red Poll cross, my only concern is the possibility of a dishonest breeder infusing South Devon genetics into stud Tuli cattle, it would be difficult to pick up a 25% Devon given the Tuli prepotence in the hybrid calves.
As always, I believe a composite should be identified as such, and pure breeds not tampered with!