Yes they are excellent. After 5 years of experience with these seats the best features are:
1. The Britax Marathon Car Seats are easy to attach securely with belts or latch anchors, and they are easy to remove. They are quick to buckle/unbuckle. You will take your child in and out hundreds of times. When your child is choking or throwing up, you will want to get them out right now.
2. The kids are relaxed and comfortable in the Britax Marathon Car seats, they often nap in them. When I bring the seats inside to switch the covers, they want to sit in them. They do not cry in their car seats. My son cried in his infant carrier, not in his car seat.
3. The covers and straps of the Britax Marathon Car Seats are removable and washable. You can order an extra cover from the Britax parts site, on ebay, or on Amazon. An extra cover is handy for washing or if your second child is a boy and your current cover is a lovely yellow with flowers. Straps can also be purchased on the Britax parts site. The seat has pockets to stow the latch anchors and rear retainer strap when not in use.
4. This seat is aircraft approved. Britax seats are the only ones i have ever seen on an airplane. Seats used onboard must be certified for aircraft use. On our last flight there were 6 or 7 britax marathons. They are heavy and unwieldy to carry through an airport, but we have brought these car seats every time we travel, and every time the kids have been content and slept. They will often sleep in their car seats in the car, but a sleeping 1 1/2 year old on a long flight …. priceless.
The distance between Sydney, Australia and Los Angeles, California is 7487 miles. It takes overnight, 14 hours. Our 1 year old slept for 7 1/2 hours straight and took a 2 hour nap in her own seat.
5. This seat will last. You will probably want an infant carrier for a few months for the convenience of taking a sleeping infant in and out of the car, but this seat can be used from birth to 49 inches tall/65 lbs. Then you will need a booster seat instead. Our 5 year old is still in her marathon. The covers have faded some in 5 years, but the seats themselves still look new.
6. The seat has been crash tested by the manufacturer.
Additional info for parents flying with small ones: Children under 2 can ride in your lap if you can hold them that long. If you choose not purchase a seat/ticket for your child (under 2), you may still bring your car seat onboard if there are seats available (check with your airline). Reclining the aircraft seat loosens the car seat and is a big help in getting it unbuckled again. You may check your car seat and umbrella-style stroller at the gate (check with your airline). You can also bring a small amount of baby food/juice/milk/water onboard for your baby (check current TSA rules). ID may be required for your little one, and passports take a long time to get, even the expedited ones.