I got a message from a user (hi @SteveJ !) who would really like to try the new generation of betas, but was concerned about losing data. Personally, I have years of data that I would never want to lose, so I totally understand this.
When you import your old database into the new beta (File > Open Database), it's actually stored in a different location to the original database. The import is a new copy of the database, completely separate from the original. In theory, after you've imported the database into the beta, you could then carry on entering the same data into both the old app and the new beta (should you be so inclined!) - they will hold their data separately.
I've made the jump to the beta with my own database - I no longer open the old app. I make frequent backups of the database in case of any issues. The beta has bugs, that's for sure, that's the nature of betas, and the old app had its fair share of issues, but the integrity of the actual data in the database is paramount.
In short, if you take frequent backups, your data should be as safe as it was in the old app. I hope that helps, but please feel free to reply if you want follow-up on this.