You are correct, the download is a trial of their Professional version of the software. Being a trial it does have some limited functionality. Here is a link to a comparison of the trial and different versions: https://www.hdsentinel.com/store.php
Both Hard Disk Sentinel and Hard Disk Sentinel Professional can be downloaded for trial purposes but in these unregistered versions some functions are not available.
The professional version ($29.95) includes a portable version or there is a link to download separately. Hint: If you download the trial version and click the register link after executing you receive a 20% discount. They state the following on their website:
The amount of computers (and hard disk drives, SSDs in those systems) is not limited - as the Portable version is used with only one computer at any given time, it can be moved to an other when preferred.