Kristian
Silicon Chip is a reputable electronics mag and their kits are normally well researched and will actually work.
I've looked at this kit a couple of times but the concern is there are no real safety features to protect the user if they mess up the settings. You can always disconnect it to revert to standard of course, but as with manually advancing the ignition if you have a distributor, the gains can be impressive or at least noticeable and there is always the temptation to push the limits for that little bit extra power.
The write up is reasonably forthcoming in its explanations and mentioning some of the pros and cons is a good marketing tool.
I believe it will work as claimed but feel that a fully integrated approach in the form of a chip is the better solution (especially if you are lazy like me).