The 1406 is an electric choke model
1405 is the manual choke model
They are the same carb otherwise. I would call the 1405 and 6 as nice reliable daily driver carbs and the Thunder series as a more performance oriented carb.
The electric chokes on the 1406 series work perfectly, and are nice for a daily driver.
If you want more control over the choke amount, duration and warmup RPM's go with the 1405 for the manual choke.