I think it is a long time coming for something like this. A few suggestions:

1) Have a setting for 2 lines for the middle pane so that all the email info can be displayed without squeezing everything so close together or having to make the middle pane a bit too wide.

2) Implement a setting so that this is user specific...My wife uses our Mac with her own user log in ID and doesn't want to use it.

I understand it is still in Beta, so I offer the above for future builds, not as a criticism.