It happened to me as well, suddenly it reported 90% health and after a Short DST health is back to 100%. I only install it when my drives are not performing as they should like random slowdowns and lags uh.. and sudden loss in data.I had Hard Disk Sentinel Standard a few months back and after checking the hard drive it told that HD health was at 16%
and it would fail in 35 days.
Well i am still here and just a week ago i did a format on the HD installing W 8.1 pro.
Conclusion: i don't trust it.
I asked a friend who repairs pc's and told me that if the health is 16% then the pc shouldn't open at all
The decision is yours Malware Test.
p.s.: Safe- Yes ,Trustworthy- i don't think so