No, they don't affect the turning radius. They are 1.25" tall round barstock(preferably aluminum or stainless steel) and with longer bolts, mount on top of the upper triple clamp, and under the handlebar bracket.
The bars will not hit the inside of the windshield at 1.25"...ask me how I know
My dad's an engineer and has a lathe at home, he made mine. They're very simple. I had him make them 1.5" tall to start, but the brake master cylinder on the right side would rub the inside of the windshield, just barely, so he cut them down.
You can buy a set from several places, and they're usually about $20.
The older I get, the more my wrists and back dislike the lean angle to the bars on most sportbikes. The bars now only being 1.25" higher may seem insignifigant, and it's not a miracle fix, but it is definately a noticeable and much more comfortable ride.
Alot of folks have them, and for the money, they are worth a try if you want to improve riding comfort.