I've been using this item for about two months now. The strap fits the leather case for my 12in iPad Pro perfectly; it's a snug fit, but it doesn't pinch the edges, pull, or crease. It holds the pencil in without fail, and you don't have to pull too hard on the pencil to remove it - it slides out quite fluidly.
The only issue I could see is if you don't have the cap connector for the pencil. This item doesn't offer a way to keep the cap in place, should it become dislodged, but if you have the connector, it plus this item is a winning combo and an excellent alternative to a separate carrying case.