What's a spider jack? From Jerry's comment I assume it's a variation on the LockJack?
I had one of those once, used it for a few months and went back to a VT hitch. The LockJack was scary in that it would release every time the rope went a little slack (pulling yourself up or stepping up on a limb). Every time you took some of your weight off your rope, you had to grab hold of the LockJack before leaning back into your rope. It slowed my climbing down a lot and reduced my trust in my lifeline. With the VT hitch, I can fall into my rope at any time under any circumstance and know that it will ALWAYS catch me. It allows me a lot more freedom to do whatever I want in a tree while knowing that my lifeline will never slip.