Trust me. Add-ons do not necessarily make things simple. In fact they can add considerable complication down the line.
If you set up a user group promotion to achieve this it works now and it works forever because it’s a standard feature. If we make changes in the future we have to ensure all existing core functionality continues to work.
If you use an add-on for this, we can’t guarantee there are no bugs, we can’t guarantee it will work in the future and if it were ever to break that’s not something we can provide support with and the solution would likely be “set up a user group promotion”.
So, seriously, avoid using an add-on for this. Get it done (we can advise how if that’s an issue) and document the process in case you or your staff need to do it again or make changes in the future.