The a1-series has always been a top-of-the-line model for Sony and, as such, had one of the most durable and refined physical designs within the system. The a1 II, though, gains a bit of an upgrade to bring it in line with the a9 III in terms of button layout, screen and EVF implementation, and durability. It's a camera built for professional use and has the strongest, most reliable design in Sony's lineup.