No. I'm afraid it is NOT legal, NOT official.
From time to time, with some of our partners a REAL, valid, licensed version is available for free.
Those can be used for unlimited time for non-commercial use.
These opportunities and links always listed at www.facebook.com/HDSentinel page to confirm that they are real and also to allow more users to get such versions.
But if a site not listed there, then they are not authorized partners and they offer the software in a non-legal way.
I'm afraid obtaining/using such versions are not fair and if they list any versions, that may cause that there will be less REAL official offers available. I'm so sad about it, but what they do is against honest users.
(because of this, I needed to remove the link from the original post.)