Disable seeing master password

I find the eye button to view master password real funny. There's no points to encrypt data and the master password is naked. It is safe on the remote storage, but not on local machine any more.

Maybe there's a way to disable showing it up, and lock out the app too?

I think you'll find that the password is for the private/public certificates which are used for encryption, i.e., it's not stored on the remote server. If you lose this, you'll not be able to decrypt your data.

There is an entry in the FAQ about (lack of) encryption/password locking of the local applications - basically the device itself should be secure in its own right.

This button to show the password was added because some people forget it. So with that button they have one chance to recover it from the keychain, provided they've previously entered it.

And as always there's the assumption that your device is secure and you're not sharing your account with other people.