Overall this product worked very well. We used it to move a 40 pound kayak over very uneven terrain. My wife found she could use it by herself with no problems. The only issues with it were:
1) No instructions on how to load the kayak
2) No picture to show how to load the kayak - on the box, it actually shows the person carrying the kayak on his shoulder!
What we figured out was you can either rest the end of the kayak on the carrier and strap it down (straps are provided) through a part of the kayak so it doesn't slide. This has you supporting half the weight of the kayak, and you have to make very wide turns. You can also rest the middle of the kayak on the carrier - you support very little weight, and you turn more easily. But when you secure the straps, make sure you don't use the strap attached to the carrier, as if you catch that the wrong way, it will cause it to collapse as you are walking with the kayak.
Overall, very good product, and it appears very sturdy.