Twin tip skis do not necessarily allow for quicker turning or spinning. The twin tip merely allows for rearwards, or "fakie" landings, takeoffs, cruising and carving, and tricks.
The binding mounting position on the skis greatly affects the ski's maneuverability while in fakie as a traditional ski's binding is normally set significantly off-center toward the rear of the ski.
Twin tip ski shapes vary greatly, and while the twin tip ski emerged at the time that the hourglass shaped ski ballooned in popularity, twin tip skis can be had in any number of widths from as little as 60mm underfoot to greater than 150mm underfoot.
Additionally, twin tip ski shapes include traditional hourglass, rockered, taper-tail and tip, and any number of other variations on traditional and non-traditional ski shapes.
Finally, the flex pattern of twin tip skis is often specifically tailored to the types of freestyle skiing typically associated with twin tip skis.
A twin tip ski will typically carve much differently than a slalom race ski, as they are designed for two different purposes.