I know a few guys with 8ightEs (running the losi esc/motor) and they love it. I also know a few guys with 8ights they converted w/ mmms and they love it.
From what I can gather the MMM is a lot more customizable and (as long as it doesn't fail right out of the box) a lot more dependable.
Based on user accounts the MMM seems to be more forgiving then the losi system for those not as experienced (at racing).
Chassis and driveshafts longer (driveshaft is actually extra long because 1.0 driveshafts popped out of the drive cups all the time). A-arms are 15mm longer, which means the wheels are now zero offset, different front spindle (has a few more adjustments), different shock towers (lighter), Rear shocks are longer, front turnbuckles are different size, steering bellcrank/servo saver is different, body is different, rear diff case is different (allows shimming). To me the biggest changes were the longer chassis and longer a-arms/zero offset wheels.