The close wound magnet wire secondary has a very high inductance per unit volume of coil form. When coupled to a large, high inductance primary, the resulting coil set will achieve the same ratio of turns transformation as the small primary design discussed previously. Yet the system is able to process power more efficiently because of the large field flux and uniform excitation of the high inductance secondary. The overall RF power processing efficiency is so great that coilers who follow this design method blow away other designs by producing bigger sparks with much less input power. The tank circuit operates at a lower frequency with less peak power which in turn reduces the stress on the gaps, caps, and power supplies.
Run times are longer with a higher duty cycle.
When something finally does fail, it is cheaper to replace. I do not like the coupling characteristics and the shape of the field flux produced by a vertically rising helix primary. I do not recommend using them unless you are building Tesla Magnifier systems. As I mentioned earlier, I like about 15 primary turns available, and the conical section should have an angle of slope of about 30 degrees starting with the lower inside turn and rising to the outside turn. On larger coils running with higher voltage inputs and greater peak powers the best primary is going to be a flat pancake.