In an update that we can call minor by Mint's standards, they have refined the interface and navigation in addition to adding a bill reminder feature. This new feature is actually quite helpful, since it can be hard to keep a multitude of due dates straight in your head.
Of course, this won't help reduce any confusion between Mint and the recently-rebranded Mint Bills service. To be clear, you will not be paying your bills on Mint; you will just be reminded about them.
Another aspect of this update is the loss of the floating action button. Before taking out your Materially-designed pitchforks, let's recall what it did: create manual transactions. With how infrequently most users do this, especially on mobile, the space the button took up wasn't worth it.
Left: v4.0 Middle and Right: v4.1
You can see from the screenshots that the eliminated FAB isn't the only change. Perhaps most noticeable (and improved) is that the system's status bar now matches the app's color scheme, assuming the black bar in v4.0 wasn't a temporary bug on my device. The hamburger menu icon and its spacing in the primary toolbar also now better conform to Material Design guidelines, as well. Also notice that on the far right screencap, you can see the toolbar collapsing and leaving just the updates and overview navigation tabs.
The navigation drawer has changed slightly as well:
Left: v4.0 Right: v4.1
The toolbar and navigation tabs now disappear when the menu slides out, which is again more in line with design guidelines. With that said, it looks odd because there is no content at the very top of the drawer. Rather than having a three-dot menu on the right side of the toolbar in the main interface, the account management and help features should be migrated to the nav drawer. The top area would be where you'd see the account that is signed in with options for signing out.
Regardless, this is a nice improvement for Mint, who rarely will let much time go by without making changes.