I use this backpack strap holder on a LowePro photo backpack with an action cam that weighs around 200 g. So it weighs about as much as a smartphone, for which a mount is also included.
It is also rubberized on all three sides that come into contact with the smartphone, which is good.
I am not convinced by the spring clamping, because with my relatively large (i.e. wide) smartphone (Samsung Ultra) I have to pull the spring apart quite a bit and that is much too tight for me.
The inside is rubberized so that the mount does not slip so quickly.
"Not so quickly" is meant literally. If I attach this mount anywhere on the backpack strap, I don't have to worry about this mount coming loose accidentally, but if you are actively out and about (over hill and dale), it does slip down a bit.
This can be prevented by attaching this mount exactly above the chest strap, as I did on my Flipside. This then reliably prevents it from slipping. This means that the camera is roughly at shoulder height.

If that works, this mount is a good recommendation.

If you really want to attach your camera to virtually any place on your backpack strap, you should go for a (metal) clamp, although good clamps are more expensive than this item.

This mount could work better with lighter action cams like GoPro than with relatively large smartphones or an Insta 360. Although the latter does produce good videos at shoulder height with this mount.