405 is more like a thin felted wool jacket. Looks more 'tailored' like a wool jacket. Has two roomy jacket-like pockets. Someone had one shrink in the wash, so you should dry clean it like you would any wool coat thing.
Shak is stretchier, moves more like a zip sweater. Drapes on you more like a sweater. Only one tiny inconvenient chest pocket in the full zip. Washes very well in the machine (on gentle of course, and gentle temps) and doesn't shrink with this care.
Because the felted wool on the 405 is a tighter density (not thicker, but just denser felted wool), it keeps wind out a bit more than the shak, but the shaks stretch and let you move around better.
The 405 has a more formal look to it and has jacket-like shoulder tailoring.