Britax Marathon or Diono Radian RXT?

My husband and I are looking for a second car seat. We just moved to the East Coast from Southern California. Our family is still in SoCal, so we'll be flying back there four to six times a year and this will be the car seat we'll eventually use once my son is too big to sit on my lap ok the plane (he's currently 11.5 months, 32in, 19 lbs) and in the car in CA. Has anyone had experience flying with either both RF and FF? We also do international travel at least once a year. So about six flights a year. I'm torn between the Radian and the Marathon. I've read that the Marathon is super easy to install and fits in most cars. If we got this one, we'd probably strap it to a rollaboard. With the Diono, I like that it folds, has back pack straps and can convert to a booster, but it's super heavy and I've read that it is hard to install. Has anyone ever used the backpack straps? I'm in pretty good shape and have hiked 100+ miles with a 50lb backpack on on several occasions, so I want to believe that I can manage carrying it; but I know it's also a different story when pushing a baby around an airport and carrying him into an airplane while gate checking the stroller (it might just be me and the LO flying back and forth to CA once in a while)! Also, has anyone had experience with either car seat in cars during international travel? Is there one that would work better?

I have had the classic britaxes (old roundabout, 65 pound marathons) and I flew with them (although i think I only ever installed them ff - my oldest was the only one I ever flew with as a toddler and he ff around 14m). I have a radian now but do not have a "modern" britax though I have played with them. I know one of the radian's claims to fame is that you can fold and travel with it but honestly it is such a beast I am not sure how many people actually do. I can't even begin to fathom how it would work rf on an airplane. You'd have to carry so many pieces. I love the radians for rf comfort and longevity but I don't think I would ever travel one unless I was out of options. A lot of people get a super light, inexpensive dedicated travel seat - the scenera used to be the one people liked for 40 bucks or so but the sure ride seems to be surpassing that as it lasts longer and is more comfortable and is possibly easier to install.

I haven't used the Radian but it can be tricky in some cars. The SureRide is lightweight and would last rf until 40" and then ff until it expires. It's very tall. The Marathon is on the shorter side and heavier but the bonus is the built in lock offs which might be useful traveling internationally.

Thanks so much for replying, this is very helpful! I'll take a look at the scenera and sure ride!

Are you planning on using it regularly in your car as well? We used a Scenera as our travel/grandma seat till DD got too big and just recently got the SureRide and the SureRide is way more cushioned. Both are nice and light for travel.

We have a Radian as the primary seat in our car and it's an awesome seat but I wouldn't travel with it, it's quite heavy. I really appreciated it each time we got home from a trip with our Scenera though as it's much more comfy. I also like the low sides on the Radian which makes it easy for DD to climb in and out by herself.

Not an expert but I wanted to share our experience with some of the seats you're considering.