in general , I think these dumbbell be great . however , they can be a bit dangerous if you do not do a safety check . for example , if you be not pay attention you can insert the pin at a angle . this create a possiblity that a plate can come loose and hit you . also , you can accidentally put the pin mechanism upside down , this create the possiblity of a accident too . I like that there be a back up system of a elastic cord and magnet hold the pin mechanism in place . I have find there be only a real danger on certain exercise and only if you do not follow the instruction . even then the odds be small anything will happen , but it be something I want to warn people about because I have have some near miss . I find the smaller version of these be better than the larger version . the large version can be cumbersome and a bit long for some exercise . however , I agree with the other review you can comfortably do a variety of exercise and the trade-off in term of a slightly smaller range of motion on some particular exercise be not a big deal . for example , for upright row I tend to prefer a short curling bar ... ditto for overhead triceps extention . however , use one dumbbell with two hand be possible and quite comfortable . this be a solid well make product . I have own mine for about a year and I think they be great . over time , there can be a issue with friction between the plate , but I very thin layer of lubricant can help . for most people , this will only have to be do infrequently .