I'm going to chime in and say that I have both a trailer and a seat and both are great in different situations. The trailer is definitely great for protection from the weather, for hauling additional gear or groceries, or an additional kid. But I first got the rear mount Bobike seat when we lived in San Francisco because I did not feel comfortable biking in traffic with a trailer to my son's daycare. It was too low, too far behind me, and we couldn't communicate with each other over the sound of the wind and traffic. I felt much more comfortable with him right behind me, at my level, and we could easily talk to each other on the ride. It's never ever felt unsafe to me, or made me feel like the handling of my bike was compromised.