I'm sold on mine - spot on.
Impossible to cheat, comfortable to use. Not only for the few shots you might take in a competition but also for practicing. It's not as stable as sitting, but more stable than standing - exactly what a kneeling position should be.
I think the WFTF have got it right with their rule change to ban beanbags on kneelers and I don't think it'll take too long before UK shooters come round to that way of thinking too. I'm convinced.