Hello,
Yes, you are very welcome to try out the free LITE version as long as you like. It is 100% free.

No payment or anything else is needed.
If you'd like to upgrade from the free LITE version to the paid PRO version, then you can do so at any time. No re-installation is needed or anything else. The "upgrade" is a simple matter of inputting a license key, which then activates the PRO features.
I do not offer a money-back guarantee, since you should always first install and try out the free LITE version. If it is good, and meets your needs, then you can consider upgrading to the PRO version only if needed. Otherwise, just keep the free LITE version and we're all happy. The only reason to purchase the PRO version is if you need the few extra features it provides.
Let me know if I can help with anything.