The download available on the Software Informer website is a 30-day trial of the product. It's a way for you to test Avid Pro Tools; in case you like it, you can then purchase a key from the developer and continue using the tool past the 30-day period. As far as I can see, there are no limitations, so it will be like using the full product.
One more thing to know is that the trial version will be connected to your iLook account, so you won't be able to install it again once the free period expires.
In case you need additional information to decide which version of the product suits you best, here's a comparison between the available editions: http://www.avid.com/pro-tools/compare
