I'm not aware of any other products that provide the same functionality within the macOS Mail client.
There are some third-party email apps for macOS and iOS/iPadOS that have some of Mailbutler's features, but my preference is to stay with Apple's Mail client, partially for …
Mailbutler is well suited to people who predominantly use their Mac for email. It adds a rich feature set to macOS Mail's native features. Mailbutler is less useful to people who frequently process email on iOS/iPadOS. Only a limited subset of Mailbutler's functionality is available on iOS/iPadOS as Apple doesn't currently provide a way for third parties to extend the iOS/iPadOS Mail app.
Mailbutler occasionally conflicts with other macOS Mail plug-ins. Though, in most (if not all) cases the issue tends to be with other plugins.
The Mail app for iOS/iPadOS doesn't support plugins, making it necessary to use Mailbutler's own app to access a limited subset of the functionality on macOS/iPadOS.
I'm not aware of any other products that provide the same functionality within the macOS Mail client. There are some third-party email apps for macOS and iOS/iPadOS that have some of Mailbutler's features, but my preference is to stay with Apple's Mail client, partially for security reasons.