With the purchase of my first dirtbike (Yamaha WR250R), I realized the pants I will be wearing have no knee protection and to me that's a must-have. My brother has a pair of Leatt's so I decided to buy the same. The 3DF 5.0 are a newer version of his. I really like them. They are quite comfortable and therefore not noticeable when riding. The cut-out in the back where your knee bends is a simple but very clever idea, as that's where material would bunch up and cause discomfort. The strap at the top of the guard allows you to keep it in place.
I recently rode in an off-road poker ride which took me about four hours over rocky, brush-filled, sometimes sandy terrain. I fell five different times and the knee guards did their job as I expected them too. The guy I was riding with asked if I got hot or uncomfortable with them while riding and I told him nope - hardly noticed they were there. I think he wished he had a set because he took a rock to the shin just above his boot. An area that for me is covered by the lower part of the knee guard.
I'm not a racer or highly-skilled rider so body protection is pretty important to me, especially since I'm in my upper 50's. I don't think you can go wrong buying a pair of these. From my age on, your knees become pretty dang precious and I certainly want to keep them operational as long as possible. These knee guards are helping me with that goal.