As an end user of all of the SNS heleicopter operators including NHV I can tell you they arent cheaper but what they do offer is a reliable service which operates to a schedule rather than when the aircraft can be persuaded to fly along with some of the pilots who like to make the rules up as they go along.
As for safety couldnt fault them, try looking at their accident / incident rate compared to the N. Denes operator????
BG