I use the Renzetti tube fly head - I find it works very well. I don't have alot of tube slippage as the surgical type tubing I use as a hook holder is attached first. I do it even before I tighten the vise, by simply holding the tag end of the thread and wrapping over it. Once the tubing is secure I push the tube back into the vise then tighten it. The compressed surgical tubing holds the tube very securely during the tying of the fly.
Even when I am not using a conjunction tube, the air brake tubing I normally tie on is soft enough that it compresses of flexes and provides enough pressure to resist spinning.
Tight lines - tyler.
Still Living Large!