The CARES harness does have a short "life span", although they were supposed to be coming out with either approval for a higher weight or a redesigned one.

The problem is that the promote checking car seats as luggage, which is a really bad idea. Even if you think your seat is "fine" after checking it, the truth is that it could have been hurled around or crushed under other bags. You never know. The seat may not protect the child in an accident. Some car seat techs recommend throwing away any car seat that has been checked as luggage.

If the children have their own seats on the airplane AND the car seat is needed at the destination, then it's best taken on board the plane. A CARES harness is good in cases where a car seat is NOT necessary at the destination.

If two parents are traveling, this shouldn't be too difficult to bring two car seats. While having the car seat is the safest way to fly, the real concern is car travel. So for me, the deciding factor would be whether the car seats are needed in Korea.

Please note that CARES harnesses can also be rented on Craigslist or on Ebay. If you buy one second-hand, ask how it's been washed (never submerged in water or cleaned with harsh chemicals). It's easy enough to just wipe them down.