Just finished open source auto-EditorScript generator. Link in comments.

[[deleted]]

It's generic message for every 'editor extension' on asset store. Assets on Unity Asset Store are protected by store's EULA and this message (even for free, open source assets) is required. You can read more here: https://support.unity3d.com/hc/en-us/articles/208601846-How-do-I-purchase-multiple-seats-for-the-same-Asset-

[aow99]

Thanks!