The cushion attaches via Velcro’s on the four D-rings of the case. The cushion fits the Oblong case with a hoodie attached. The cushion is very spacious, it can fit a very reasonable amount of music including the Bach books. It even holds the 15” MBP, so I can bring my laptop with my violin without an extra laptop bag to do business. The Velcro’s seem to be very sturdy and of good quality, it should hold even when many items are shoved in the cushion increasing the weight, but not all four of the Velcro's would detach so its no worries.
The item is quite expensive, but that’s the price for a nice quality cushion and pocket for a very nice Hightech case. I wish before I bought this that there would be more photos describing the item, but the team at GreatVolinCases was great and answered all my questions swiftly. The cushion is quite tall and sticks out of the case.