The cabinet will almost certainly fit your short bed 301, but you will need the 301 cradle and the two latches that prop the front of the cradle. (without the two latches, the cradle has nothing to hold up the front and keep the machine upright)
The 306 will be a more powerful machine than the 301, and with the vertical needle, it will give you less trouble with needle deflection. It's a decent free-motion quilting machine and it could become your favorite for FMQ, depending on what you're quilting with, now.
Its usefulness is relative and depends upon what you already have in your collection.
