I'm a fan of Atmel more so than the Microchip/PIC stuff, but ever since they've merged, I'm seeing features cross between the two chips. MVIO is basically a level-shifter. You can run truly 5V on some I/O, while running the core voltage at 1.8V (minimizing power usage). Not just "compatible" with TTL levels, but truly outputing 5V (very good for driving 2N7000 or some other MOSFETs).

A note: the "Curiosity Nano" headers are offset in a zig-zag pattern. Microchip does this on purpose, you're supposed to bend the headers into place (ie: shove it in there really hard). The friction and tension will allow you to use the headers even if you don't have a soldering iron. And if you do have a soldering iron, the friction/tension will help keep the pins straight (erm... zigzag??) and make soldering much much easier.

Its definitely a superior way to use headers. But its non-obvious the first time you buy a Curiosity Nano board.