It's not really fair to call Maxwell a "slow" renderer. Imagine if you were using Mental Ray with GI and Final Gather, along with full caustics, a gazillion photons (pretty sure gazillion isn't a number ), and the highest quality anti-aliasing settings possible, well it would take an extremely long time to render an image also. Maxwell basically does the same thing, but that quality is Maxwell's default setting. You do have the ability to turn off some things, such as the level of caustic reflections, but in general you are indeed stuck with rendering at the highest quality settings whether you like it or not. It's not a practical renderer for animation, but that doesn't mean it isn't used for animations. As with everything computer related, speed is merely a function of how much money you're willing to spend.

Here's an animation studio who uses Maxwell in its pipeline:

www.keytoon.com