Diziana provides many of it's theme for free. There is no difference between Free and Premium version in terms of quality, and features. Free version of theme and plugin can be used anywhere as long as licensing terms (attribution is required; not to be used on fully private help-center).
A free theme can always be converted to premium with the purchase of license; no code or design needs to be changed. A license would grant you rights which free theme license doesn't have.
A Diziana Premium Theme:
- Can be used on fully private help-center
- doesn't require attribution (credits) to be in footer of help-center
Please refer to Licensing page for more information.