Best car seat for international travel - 18mo child

We currently have a Britax Marathon as the primary car seat for our 17-month-old. In a few weeks we'll be traveling overseas and bought him his own seat. Originally I figured we'd just haul the Britax with us but as the trip gets closer I've been thinking it's just going to be too bulky and heavy to schlep around the airports, so we're looking to buy another seat that will be easier to travel with, and can also serve as a secondary seat at home.

I've been looking at the Combi Coccoro and the Evenflo Tribute - any thoughts on flying with either of these? Or recommendations on other seats? Cost isn't a huge issue...obviously saving money would be great, but we're willing to pay a little extra if it means he'll be more comfortable and more likely to sleep for part of the flight, or if it's something we'll get more use out of once we return home.

He currently weighs about 26lbs and is around 31.5" tall, with a very long torso and short legs.

Keep in mind that cars in other countries don't have locking seat belts. The Britax would be nice since its got lock offs but it is bulky, I will add that I've heard good things about their travel caddy. If you're still rear facing the combi allows European belt routing so you wouldn't need locking belts. Otherwise anything you bring will require a locking clip.

Do locking clips come with the seats or is that something that needs to be purchased separately?

Does the Corccoro come with built-in lock-offs? You wouldn't need a locking clip for it.

In my experience, the carseats that we've owned that don't have built-in lock-offs do come with a locking clip. I've bought a couple spare ones as well, just in case. I've actually given them to friends who didn't realize that their cars don't have manually locking seatbelts (we live overseas).

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=locking+clip

The Coccoro has built-in lockoffs for forward facing, and a separate-but-included lockoff for rear-facing. Even with the around-the-back seatbelt routing, a lockoff is sometimes required. It depends on whether it holds tight without it, which depends on the individual seatbelt.

The Coccoro is a very different seat and can be unusual to install until you get used to it. I've used it in a ton of cars and have only had trouble in two, and in one of those I had trouble with other seats, too, so I don't blame the Coccoro for that one. It is a fantastic seat for traveling because it's so small and light.

I've traveled with Britaxes, too, and they're fine but much heavier and bulkier.

I'm also a big fan of the Radian for plane travel. It can fold and be worn as a backpack if you have two carry straps (available for purchase). It might need to go forward-facing on the plane, but in a car it will last longer (rear- and forward-facing) than a Coccoro or Britax convertible.

I've traveled with a Marathon and it's actually a great seat to travel with. It's compact, so it fits everywhere, it installs on the plane really easily either forward or rear facing, and it's got lock-offs so you're set. Bonus you're already familiar with it, as is your son. I'd grab a folding luggage cart from somewhere like Walmart for $15 and you're set. You will probably have to lift it up over the plane seats when loading, but flight attendants have been very helpful to me if my hands are full. If you get a sturdy cart and attach it securely you can strap your son into it and turn it into a stroller.

We don't have Cocorros in Canada so I've never used one so I can't say how much use you'd get out of it long term.

If you were wanting a second seat for at home that's a whole different conversation I think, especially for long-torsoed kids. A rear-facing Radian isn't fun on a plane, and then if you're getting into a tight fit in a rental car and possibly carrying an angle adjuster with you...too fussy for me. They're super forward-facing a plane, and can be an easy install in many cars but in others it can be very challenging.