The zigzag attachments are not accurate at all. You will never be happy doing anything that requires accuracy.
I have both the 301 and 401 and it's really like comparing apples to grapefruits. You need to decide if a zigzag is necessary and go from there. The 401 does straight line quilting fine, but it does NOT free motion well at all. So, if this will be needed, you should also think about that.