An imbalanced sound can make an otherwise good guitar unlistenable. We've all heard it; highs that are piercing and borderline painful or lows that become indistinct and mired. The Duo-Tron design addresses these issues in a manner that can only be achieved by the unique design of these pickups.
The blade of a Supertron gives greater voice than individual pole-pieces without the darkening effect of more winds on the coil. Individual pole-pieces, conversely, soften the notes slightly in comparison to the Supertron's bars. By strengthening the lows of the bridge pickup and the highs of the neck pickup, the Duo-Tron bridge is designed to achieve an unusual degree of balance between the highest and lowest note.
At the time of this writing, I have had significant experience with only the bridge Duo-Tron, so I will confine my comments to it.
By having blades on the treble side of a bridge pickup, the lower three strings are accentuated while the upper three strings are cooled down just enough to avoid the "icepick" effect which can occur on the highest notes. The lower notes are powerful and clear while the upper notes are twangy, but not unrestrained.
The overall effect is an unusual degree of balance. I recorded a Surf tune using the bridge Duo-Tron on my G-6119-1959 and the balance was stellar. The lower notes were powerful, yet retained their full definition. The upper register notes (well above the 12th fret of the 1st string) were powerful without being overpowering. The result was very close to something you'd hear on a classic Surf track from the '60s.