I guess your experiences might be due to not having a perfect match between your halyards diameter and the cleat. As I wrote above, we had to sleeve a 8mm hose over our 6mm halyard to make it stay in the cleat.
It's possible. It seemed like a decent quality device, and was mounted on a metal plate and had a bridge across the top, so I don't think flexing was the problem. We couldn't explain it at the time.
I've not had any reliability problems with the spinlocks. They also have the advantage that they never accidentally cleat the rope when you're dropping the spi.
Paul
