Give HideAway VPN a shot. According to them, the trial is fully functional and begins with 12 hours of free usage, which decreases gradually. It's not limited to a specific number of devices. Windows is the only supported platform right now.
Here's how the trial worked when I tried it:
The starting point had a duration of 12 hours.
You'll have to wait for 10 minutes after 12 hours have passed. Two buttons will appear: "Use Free" and "Buy Now".
Pick the "Use Free" option. The 12-hour time frame is once again the starting point.
I don't have any idea about the trial's duration. The "Use Free" option consistently gave me either 6 or 12 hours. The trial never ended, even though I used it for almost two months. I recently took advantage of a heavy discount on StackSocial and purchased a lifetime license.