The case feels solid and well-made. I would have no trouble throwing this in the overhead bins on an easyJet flight.
I don't care too much for the backpack option as the outsides of the case are solid plywood boards. This is not very comfortable. To me this is secondary to the amount of protection it gives the guitarlele.
I have a guitarlele that I bought when on holiday in Indonesia, so the body shape is a little bit different from the norm. So the I modified the case to suit. It wasn't hard to do, but it did show that the case was well put together. A knife is all you need to shape the foam underneath the fabric. This is probably a non-issue for anyone buying a standard Thomann Guitarlele.