This is a quality, sturdy bag  good zippers, wheels, and handle.  The side zipper pouch is big enough to stuff a jacket in while wheeling at airport.  It is expandable (but then would excede new limits).
However, note it is advertised as 21 but that is  just the length of the bag.  If you add the length of the wheels, it comes in at 23 inches so if gate personnel wanted to fuss, they could.  Comparing with the IT Los Angeles carryon model I also got, which is truly 21 inches,  it is 1.8 lb heavier and bigger, but will last longer. I will keep both.