The Kolcraft Contours Options Tandem handles very well. I never felt like I was in any danger of tipping it over. The seats are well-secured, and by that I mean 5-point harness (as recommended by experts). I’m not an engineer so I can’t give any real specifics, just my personal experiences and observations.
The Kolcraft Contours Options Tandem really took the word "Options" to heart. I could have had newborn twins, and this stroller would have worked for us. The stroller accommodates a wide range of car seats, not just brands but sizes. So when Aidan was one, I had his standard seat in front, and Keira’s infant seat in back. She was facing me, he was facing forward. I could have had them facing each other. There are actually six options, and we’ve tried most of them! Now that Aidan’s older, he likes to walk a lot. But we still bring his chair in case he gets tired or needs a nap.