REST API - public endpoints question

https://aboutcode.readthedocs.io/projects/PURLdb/en/latest/purldb/rest_api.html says:

> We maintain also public endpoints at https://public.purldb.io/api/

Are there any terms of use, or SLAs, for those public endpoints? Would it be allowed/advised to use those APIs "productively", for example to validate and check the existence of a purl via https://public.purldb.io/api/validate/ ?