If you're not comfortable with some of the "knee support" style crutches on the market, the oneCrutch can let you slowly learn to use just "one crutch".
For example, you've just been released from the hospital and someone offers you an iWalkFree or Knee Walker trolley. Maybe you would rather stick with regular crutches for awhile instead of trying something radical/expensive like these devices. With the oneCrutch knee crutch attachment this is possible. With it attached to YOUR crutch, turn the attachment so the platform is on the outside and use your crutches like normal. As the days progress you can turn the crutch so that the attachment is on the inside. Now you can (when you feel comfortable) place your knee on the attachment and slowly move some weight off your armpits and on to the knee of your injured leg. As more time passes you can eventually lose the crutch on the non-injured side of your body and place your full weight on just one crutch, thereby freeing up your other hand to carry coffee, magazines, etc.