First issue. The straps will not last long. At first glance, this is apparent. Upon use, it's even more apparent.
Second issue. The shoulder straps don't do much in the way of providing protection from the pull of really heavy weight. This could have been remedied with $10 worth of stitched foam.
Third problem. There's no way you could use this on any other surface than grass. Even then, the hooks holding the straps to the sled are beginning to show fatigue after some light sprints with only 60lbs.
Anyone serious about working on their sprints should look somewhere else.