JDownloader 2 updates frequently. An unofficial plugin for a private database will break every 2-3 weeks. You will spend more time hunting for updates than actually downloading.
Many modern databases use "Session Cookies" instead of raw usernames and passwords. This allows multiple people to share one premium account without triggering security alerts that lead to account bans. The Risks of "Exclusive" Databases jdownloader 2 premium database exclusive
[Solved] Forcing using premium account - JDownloader Community 14 Dec 2015 — JDownloader 2 updates frequently
Your JDownloader 2 instance is Java-based. Many "exclusive database" plugins are trojans. They don't just provide premium links; they also scrape your saved logins for your email, cloud storage, and even cryptocurrency wallets. Many modern databases use "Session Cookies" instead of
Adding your credentials to the "Account Manager" is the standard way to activate these benefits. Jdownloader2: What it is, How to install & How to debloat
Use premium accounts only for content you have rights to download. Respect hoster terms of service.