I live in a hilly area, I commute everywhere on a fixed gear.

Commuting Fixed Gear is a little like driving in the snow with a manual transmission or limited slip differential. Without the freewheel, you'll have the ability to feel when your rear wheel is losing traction in the snow, usually far before it causes a handling issue, so it's probably closer to limited slip.

You can feel the loss of traction on any bike, but in my experience I'm able to sense it alot faster on my fixed gear bike.