Airport strollers turn travel into a balancing act—gate-checking exposes gear to rough handling, hauling a stroller through terminals strains your back, and wrangling kids while clearing security feels like a full-contact sport. The TernX Carry-On Luggage Stroller aims to fix all of that, shifting from a compact stroller to overhead-bin-ready luggage in seconds. It’s a clever solution, though the $699 price means it only makes sense if you’re flying often enough to justify it. Real-World Performance, Not Just Marketing Claims Hands-on testing shows the concept works, with a few caveats. The folding system does exactly what it promises, but there’s a learning curve. In independent trials by ZDNet during a New York–Indianapolis trip with two young kids, the three-step conversion (triggered by button presses) became second nature after a few runs—but it always requires both hands. That detail matters when you’re juggling a toddler, a boarding pass, and a bag at TSA.…