I thought case liner bags were a waste of money ... till I bought a set.
If it fits in the bag, it'll fit in the case. Makes packing and unpacking very convenient.
These bags are semi-rigid and form to the cases very well. To the point of having to work the bags into the case even empty.
On my wish list ...
Some organization pockets. There are external side sleeves, but putting in a phone charger and cable makes it difficult to slide the case into the cases.