My only tool for right handed use is the scissors. They are really hard to use with the left hand. Even my custom made knives are designed for use with either hand.
Using tools with your weak hand depends on the amount of practice you have and how dominant your strong side is. I´m almost ambidextrous. When I have to use tools with my weak hand, it usually takes only a short time to switch. People who lack pratice or have a very dominant side often can hardly use any tool with their weak hand because of that.
I´ve handled knives that were designed for right handed use. The were useable with the left hand but it felt very unconfortable and it meant to sacrifice some power and precision.