When set up properly and used with OEM specification belts the 2 belt system is head & shoulders better than the single belt version .
It should give a substantially longer belt life .
The chords in the deck belt need to be deep in the belt to allow for back bending.
The chords in the drive belt can be right up the back where they provide maximum tensile strength .
You can use lighter more responsive tension springs with longer travel because there are two of them .
Down side it is more expensive & the mower market is very price sensitive particularly at domestic level
