Wanted a hard case to hold trumpet + mutes + random bits and pieces, which was backpackable and airline carry-on-able. This was the closest I could find for a reasonable price. In fact, it fits all those criteria apart from that I think technically it's marginally over most airlines' dimension limits but I've flown with it on a couple of trips now and haven't been challenged.
To make it a backpack you need to purchase the Protec backpack strap. I did, and usually carry the case this way, and regularly cycle with it on my back. (For cycling I recommend buying some reflective stickers to be visible on the road from behind!)