Guy's,
This beat up on Spartite does not make sense. You are lambasting the product for doing its job and doing it very well. With proper foresight and preparation as with everything, Spartite will let go your mast when it should.
The key is that at least one surface (the one that will let go) should be very smooth and have a taper. That surface must then be waxed and over the wax I also apply Vaseline (just to be damed sure) before you pour the Spartite. Since you will not have access to the parts in question once the mast is in, you need to take care of this before you step the mast.
If you build your mast as per PJR, the buried portion will have a taper and its in the right direction. If your mast is parallel sided or it tapers from the base, your partner then needs to be tapered. The taper should be such that the larger opening is on the deck side and the smaller opening on the inside.
On PJR style masts, the mast side is the one that must let go. On parallel sided masts or mast with taper from the base, the partner side is what must let go.
If you follow the above rules, you will love Spartite as it does its job wonderfully well and your mast will still come out when you want it to.