Under the hood, Prepros 6 is a completely different app so you can install Prepros 6 and use both Prepros 5 and Prepros 6 at the same time. Prepros 6 can also import config from Prepros 5 while adding project.
Prepros users who purchased Prepros in last 4 months can get upgrade for free. Other users can upgrade for $19.
Prepros trial is unlimited but it pops up a trial dialog on startup and at some time interval. You can buy Prepros to remove the popup. There is no other difference.
You can use free version forever but It will open a popup asking you to pay. You can disable popup by paying for a license.
If Prepros is not showing compile notifications on Windows 10, Please go to settings and make sure notifications are enabled.
Please use the following links.
You can retrieve your key from Prepros Shop. Click the lost key link on the footer.
Contact me at my email address hi at prepros.io.