I have been a 1Password user for a couple of years now. There are multiple reasons for that and one of those reasons is their nerdy openness. But also their constant innovation, like how they totally modernized their latest version of the app.
Posts like these in where they explain why they move to 256-bit AES are great.
The performance concerns that we had in the past—both speed and power consumption—are no longer a concern today.
My conclusion is that the most important reason is that the mobile hardware is now able to handle it well, which enables all the other reasons.