The reason we developed it is because 3.7 uses different authentication algorithms and approach from 4.x. The alternative option was to migrate the users in the default provider but with new passwords and then reset the passwords for all users from 3.7 which was not a good option, especially for sites with many users. With code you can "move" the users to the default provider but they'll not be able to log in and will have to reset their passwords. However, you cannot make the OpenAccessMembership37Provider the default one. You will either have to use both providers (this is recommended and causes no issues) or move your users to the default provider, losing their old passwords.