Is this bag accepted as a carry-on by major airlines?

At 21 inches it is sized for most US domestic carry-on limits. Check your airline's exact dimensions, especially if you expand it, since expanded bags can exceed sizer frames.

Does it have a TSA lock?

Yes. A built-in TSA combination lock lets security open the bag without cutting it. Set your own combination before your first trip.

How much does the expandable section add?

The expansion zipper adds roughly an inch or two of depth, enough for a few extra layers or souvenirs. Packed full and expanded, it may not fit tight overhead bins.

Is softside better than hardside for this bag?

Softside gives flex in tight bins and exterior pockets, but hardside shells resist rain and scuffs better. Choose softside if you value give and organization over protection.

What is inside the main compartment?

A divider and packing straps keep clothes compressed and organized. There is no built-in compression packing cube, so add one if you pack tightly.

How does it compare with the Montecito 2.0?

The 3.0 updates the wheels and hardware and keeps the expandable softside design and TSA lock. If you already own the 2.0, the upgrade is mainly in rolling smoothness.