I have one and have used it a lot. It's brilliant and the only limiting factor is how high or for how long you can lift a board. I've got the larger one and you can clamp two boards together if you can lift it.
The clamping action works well and obviously clamps harder the heavier the board is. I've never had a board slip aside from when I'm trying to move a board onto a table, for example, where I momentarily ease pressure off the handle. So keep the pressure on by lifting and it's rock solid.
I've used it to shift boards in and around the workshop and I even carried a couple of 12mm sheets of plasterboard back from my local Travis Perkins who are 10 mins walk up the road - never again - I bought three and told them to sod the third one.
If your use case is for moving boards on edge around the shop then fine. But if you want help maneuvering sheets from vertical to horizontal onto a table for cutting, then it's not perfect, but with a bit of technique should be easier than not using it.
