OK so how effective are they, and whats best way of delivering them and where is the best part 2 deliver them 2?
Tough to say, depends on how the clinch is going. Is it an effective move? Absolutely. People forget to charlie horse their opponents sometimes so go for it. Just don't forget with your knee low, you are leaving some upper space open and you may not be able to block if he goes high for the waist or ribs. Like anything else, strike hard and first.
mike kyle landed a knee to justin eilers knee and groin then justin koed him at ufc 49. so knees to the knee can work but make sure you land more then 1