The problem likely has to do with sytem priviledges, and not the installer. This has been tested not only on my multiple systems, but on MANY other computers. Why it would work fine there and not on your system suggests your system. No one likes to hear that. However, if it is as simple as the fact that there are not priveleges for installers to write to the targeted directory, then it is your system, and not the installer, and it really isn't a big deal. I test it every time someone has a problem--though I am quite sure by now that it works. The same identical package is used to install the tools in the custom installation, it is just initiated in a different way. The initiation just allows the user to target a directory, rather than picking it for them. if that works, the installer is likely not a problem.
The instruction on screen for the mac discuss deleting cache. Troubleshooting on the website discusses it as well. There is significant documentation...and while that is not to say it can't be improved, I am not sure what to add, and I am pretty sure it states that after installing the cache has to be deleted--and it is ordered that way by the installer, and in the custom installation listing for options.
The installation is hopefully the most frustrating part for you. It has become the rare case with Hidden Power (now in its 3rd incarnation) that there are installation issues of any kind...i also rarely get the accusation that there is no real product to sell ;-) Now if I could just tackle the problem with people downloading with the wrong type of browser, I'd have very few support emails to answer!
I look forward to hearing about questions on using the tools -- there are far too few of those.