It's certainly good that SpaceX uses many ways to test hardware, including those approaches successfully used before. During development of F-1 some interesting debugging techniques were invented, some could be well applied in SpaceX.

Gas generator cycle in general doesn't allow reaching effective Isp as high as closed loop cycle. On the other hand, smaller pressure reduces stress and generally considered safer. NK-15 were single use engines, but NK-33 and most other modern engines are all reusable.