Just a quick update. Lax - ewr RT. 757-200. Two Britax carseats. Both wouldn't fit down the aisle empty, much less with a squirming toddler.
Also had some trouble with the carseats shifting and hitting the wheel. Had to adjust them most times after switching from upright to rolling position.
All in all made it easier to get the carseats through the airport, but we still needed a stroller, to help with the bags and stuff, and for my 4 year old who doesn't like walking, and $150 is a lot of money.