It's going to depend, at that age, on their ability to sit still. My kid couldn't; perhaps yours could (although parents often find booster behavior is worse when more than one kid is in the car.) I'd test them out before planning on using one.
As for travel boosters I'd probably bring something like a Graco Turbobooster, because it's cheap, and the back detaches. I'd pack the back, well-padded, in my suitcase, and carry on the base (with adjuster strap just in case.) That way if something happens to the suitcase with the back, you still have a booster to use.
I'd also consider the Ride Safer Travel Vest for kids that age who can't sit appropriately in a booster. Yes, it's going to run you $200. But, you can use it in cars without the top tether if necessary, unlike the GO (if you ever ride in a cab or non-rental this may be an issue) and it's much easier to carry than the GO. You could literally stuff both in your carryon, with no issues.