Rod tube is probably the best way to protect your rod nowadays. Tubes are extremely popular among fly anglers, where very often the tube is sold together with a more expensive rod. Spinning and sea anglers also use tubes, as well as world-traveling anglers. A decent, specialized, large tube is the best way to transport the rod on the plane.
The tube is definitely harder than the usual, even additionally stiffened rod bag, however, it is not suitable for transporting all types rods.
The main limitation of the rod tube is its diameter, i.e. rods with large guides are problematic and do not fit inside. However, tubes with diameters above 10 cm are already appearing on the market, so it will be better.
Tube for a rod with a reel is a product that can satisfy many spinning anglers, because it is them they usually buy this version. It is just something between a tube and a bag and allows you to transport a practically ready fishing rig. We take it out of such a tube, assemble the rod and fish.