I read up a little on this thing. It seems to get satisfactory reviews, and it's sold by several retailers that I trust to not sell useless or worse products.
That said, +/- 5% accuracy is not good enough for me, and I have serious doubts about even that consistent level of accuracy.
I calculate the weights of loads by knowing the manufacture's weight specs of equipment, trailer weight, etc. I also weigh the tongue with a small hydraulic scale.
With my RV, rather than weighing individual loaded items, I loaded the trailer for use, then took it to the scales.