I installed the demo just to check it out. I've been using the version for AE for a long time, and it's nice to not have to jump out of Final Cut to AE just to run the bullet on footage...
I have it too, and noticed long render times as well. Avoid the effects that create softness, this uses bluring and that is what makes it take so long.
I feeel that Magic Bullet editors is faster anyway in FCP than in After effects. I have use it and I like it too. The presets are litlle bit childish, but you can create your own set ups.
I think it rocks...