This GURPS supplement is derived from White Wolf's Mage game, from when that game was in its first edition. It adapts White Wolf's much more free-form magic system into GURPS mechanics. It's not really compatible with the (then) pre-existing magic system for GURPS, as this version is far more powerful, and if your GURPS game mixes genres, old-style wizards and magic-user types are liable to feel ripped off, as they will have paid more character points for less power.
I feel that this adaptation captures much of the feel of the original White Wolf game, while adding the ubiquitous game-mechanics of GURPS in an appropriate manner. Much of what makes the White Wolf version hard to play is the absence of hard-and-fast system rules. The GURPS version attempts makes up for that without eliminating the open-ended feel of the original magic. In the end, a compromise is reached. This version strikes a balance between total game mechanics-oriented and free-form story-oriented magic.