I am not entirely sure why duro test did that, but i like them

The twists in the glass increased the surface area of phosphor leading to increased output for the same arc and same wattage.

The thing is, the plasma in the arc generates UV, but the mercury around absorbs it.
For high efficiency generation you want low current density, so for certain power so intensity it would mean large tube cross section, so large tube diameter.
But with large tube diameter it means, the path for the UV generated in the middle of the arc to the phosphor is long, so the absorbtion eats a lot of it.
The flat (or flower) like cross section shape was in fact an attempt to make the cross section shape so it still has sufficient cross section area, but the distances are small. But a flat tube means the light intensity would be different in each direction, so it won't match the standard fluorescent pattern. To solve that, the maker just takes the flat tube and twisted it along the tube.
Same objective was reached by other maker by forming dimples in the tube (so the cross section was like "C"), to maintain the directional uniformity, the imprints were shorter and alternating from both sides. The different patterns among different makers were because each maker had their exact pattern locked by patents, so the different shaping for the same goal was just a way to go around each other patents.

Modern tubes solve the problem by altering the buffer gas mixture and phosphor materials, where the discharge maintains the efficiency even at higher current densities (and related higher wall temperatures), so the tubes for the same output could be made thinner (started with T12->T8 and most modern with T5HO), so the complex tube shaping was not needed anymore (it would still improve the efficacy a bit, but the difference would be very small, by far not worth the high cost and extreme fragility of such shaped tubes).