Bipes are also a bit harder to see in the air. Depending on the model, the extra wing can really play games with you and what you think you're seeing. Someone on here had a great example where they took some image files of a monoplane and a bipe turning, then turned them into black silhouettes. With the bipe, it can be really hard telling what is going on if you aren't paying attention.

Still, have a soft spot for them. I don't care much for the looks of the Ultimate myself, but the Model 12 and some of the Waco and other golden age bipes are a lot of fun.