I'm using this with a Safety 1st Onboard 35. The basic concept is pretty good... but this really does not work with a larger car seat. Don't know how it would be with a smaller one, but for a 35 pound capacity bucket seat, it's downright unsafe. Once, when I did not have a good grip on the seat itself, it pivoted, and if my baby hadn't been strapped in he would have been on the ground.
As it is, it merely provides a little bit of weight distribution, not the hands-free capability I am used to from the Stay In View I used with my older child. That carseat had an integrated foot-to-head strap and no hard handle at all (much preferable.)
This strap tends to slip and turn and move, cannot be fixed with the strap in one position on my car seat. Because of how my car seat is designed, if I position the straps the way they are in the picture, the whole thing is "top heavy" and will pivot toward the baby's head, which is worse than useless. And the straps are not stable at the top of the carrier, nor can I put them on the inside of the handle, which might make things more secure. I can't tighten or lengthen the horizontal strap across the top, and it's either too big or not big enough for stability.
It is marginally better than carrying the thing by the handle alone, but mostly the only time I use it is to get the carseat into and out of the car at home. It makes a decent strap for the empty carseat, but requires too much attention to be really useful for hauling the baby.