Rule of thumb: Whenever you think you don't need relational database features, you will later discover why you do.

The one thing relational databases don't have, that you might need, is scaling. Maintaining data consistency implies a certain level of non-concurrency. Conversely, maintaining perfect concurrency implies a certain level of data inconsistency.

The other thing relational databases don't have, that you are definitely going to need, is a practical implementation.

You could maybe consider Rel if you have a particular type of workload, but, realistically, just use a tablational database. It will be a lot easier and is arguably better.