I think clarifying the difference between a PAC and a super PAC will be helpful. A super PAC can accepted unlimited donations and can spend unlimited amounts, but only on certain items like advertising or lobbying. A normal PAC can make direct contributions to individual candidates. As described in the article you mention, super PACs are less effective than donating to individual candidates, but donating to a normal PAC can be similarly effective to candidate donations, provided the PAC is aligned with an effective cause.
It sounds like GAP is a hybrid PAC where one pot of money can be treated like a super PAC (unlimited donations, unlimited but restricted expenditures) and the other pot of money is treated like a normal PAC (limited donations, able to contribute to candidates). If you were to help fund GAP, your money would be going toward the latter pot.