What characteristic defines French type haircutting shears?

The defining characteristic of French type haircutting shears is the presence of a one finger brace. This design allows for more flexibility and control while cutting hair, as the one finger brace fits comfortably around the finger, facilitating a more natural grip for the stylist. This design is particularly advantageous when performing detailed work, where precision is crucial.

In contrast, options such as dual finger braces, offset handles, and tapered blades describe features typical of other shear designs. Dual finger braces allow the use of two fingers for a different grip style, which is not characteristic of the French design. Offset handles are more common in ergonomic shears designed for comfort during extensive use, while tapered blades refer to the shape of the cutting edge and not specifically to the finger brace structure. Hence, the one finger brace is the key distinction for French type haircutting shears, making it the correct answer.