Ok girls and guys, I also bought the bundle.
Everything seems to be fine.
Except for the fact that even when you have the license key you need an active Internet connection to validate your copy of Poser 12.
But that is just what I consider a bad habit too many companies have.
So, to recap how it works:
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You may create accounts at these sites, but this is not required.
Your email address (and some billing data for Graphixly) will suffice.
So, you buy at Humble Bundle
There, you reveal a coupon code
and follow redeem instructions there...
You land to graphixly and put the product in the cart.
You apply the revealed HB coupon and the price is zeroed.
Completing the procedure will give you a Poser 12 license key
(they send you a couple of emails)
Then they send you to Poser Software
where you can validate your key and download the Poser 12 installer (not the content ones)
Install the program.
Ok, now let's say that you have your Poser 12 up and running...
You can install all the included content from inside the Poser Library (very convenient, I did it)
But if you want to also have the offline content installers (I definitely want) you go here
Poser - 3D Rendering & Animation Software
and at the bottom of the page you find the links to download the offline .zip files for manual install
(requiring your License key to access)
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I hope you have a fast Internet connection because all this stuff is around than 22 GB (including content)
But above all I hope this helps anyone who may be interested in buying this bundle...