I purchased a set of Nuobell S 5100 black. I am quite pleased with this decision. I choose these after much comparison and research. This set had all the things I was looking for in an adjustable dumbbell. The shape and weight distribution more closely resembles that of a traditional gym dumbbell. The weight feels and moves naturally when held unlike a skeleton frame or a box you put your hand inside. The way the weight is adjusted is a plus. It only needs a simple twist of the handle to increase or decrease weight, which I preferred over any knob or pull/push pin design. In addition the changes happen in traditional five pound increments not odd weights or half pounds. Once I decided on the Nuobell brand I began exploring their products. I chose the S 5100. This is an upgrade of the original with its internal parts being more metal than plastic. The maximum weight has increased making it one of the heaviest dumbbells out there. I chose the hundred pounds over the sixty pound. It will be quite some time if I ever reach the highest weights. However I am confident some of my exercises will pass the sixty pound mark. It made sense to buy the S 5100 now, rather than purchasing the weight upgrade later that would total more than just buying these. I purchased these directly from their website and was given a four year warranty. Nuobell also has replaceable parts on their website. They were delivered within one week and were all well packed inside. There were four boxes total. I have used these several times now. I do not hit them together or drop them. That would not be a good idea for these or any other adjustable dumbbell. I have the pylon stand for these as well. They look nice and save space. These are expensive, but worth every cent. Buying all the weights they offer would cost three times as much and would require much space. Overall I am extremely satisfied with this set and plan to use it for many years.