Hi,
The new monthly payment option allows you to download up to 100 Substance textures per month for $149.00. You can start and stop the payment anytime. If you stop, then you keep the Substances you downloaded.
You own them and can still use them : )
Full payment gives you instant access to the full Database or you can pay the monthly until you’ve paid the cost of the full database price.
For the interactive web preview and list of the substances, check out the site.
https://www.allegorithmic.com/products/substance-database
Substances can be used directly inside UE4.
Cheers,