yes,but there's this:
Q. Do I need permission from my airline to use CARES?
A. No. CARES is certified by the FAA for use on all US registered airlines. Parents have the right to bring CARES on board for their children
this:
Q. Can CARES be used on overseas flights?
A. Yes, if the flight is operated by an American carrier. Most countries automatically accept FAA certified devices (like CARES), but you should contact the foreign airline prior to traveling.
this:
Q. CARES is a new product. Will airline staff know that it is allowed on planes and how it works?
A. The FAA, aviation trade organizations, and the airlines are all working hard to disseminate information about CARES so no one will be surprised when CARES begins to show up on planes. These organizations are conducting in-house training programs and rewriting internal procedures manuals for all airline staff, from safety officers to flight attendants, pilots, gate agents, and ticket agents. They are explaining that CARES is an FAA certified alternative to a car seat and that parents have the right to bring it onto planes for their young children. They are also updating their websites and published information about traveling with children. By the time you have your CARES, all of the airline personnel you are likely to meet SHOULD (emphasis mine) know about CARES.
and this:
Q. May CARES be used on all aircraft seats?
A. CARES is certified for use on all US registered airlines and the vast majority of aircraft seats. There are, however, a few exceptions. CARES must be used on front or aft facing seats (not on side facing seats); CARES may not be used on a type of older style seat, still used on a few smaller or older aircraft models, that has a recessed tray cavity with rigid sides into which the tray fits when closed and which will not accommodate CARES; and CARES does not fit on sleeper seats and may not fit on the largest first class seats or the larger seats in executive jets.
In the theory, a good idea, and certainly lighter than lugging a carseat, but please expects hassles.