[suicideneil]

You dont wanna know what I think about most of the time....

No good reasons to go with 2speed really, unless you have an underpowered setup, or an outrunner that needs a low gear ratio to get spinning properly before switching to high gear.
Yep, steel idler, and concider 'fixing' the input shaft issue- the roll pin that holds the input gear onto the input shaft is known to break easily with BL power, so you can replace it with a hexkey or drill bit which you press into place, before cutting it down to size and gluing with a drop of loctite. You can also use a revo input shaft and trim that down to size to fit the single speed conversion, then you get to have a 3.3spec slipper, rather than the stock emaxx one.

As for the MMM, it is shaping up to be a really good system provided the Neu type motors perform half as well as proper Neu motors. The inital motor it comes with is looking like a 1515 1y item, good for 4s, or 5s for speed runs. Slower motors for higher voltage will follow soon after apparently, so anything from 4s-6s will work beautifully depending on what you are doing (bashing, racing, speed runs etc).

Only other weekness to speak of are the revo diffs, but with an alloy diff cup they seem to do well (removes any flex between the spider gears). Only other upgrade to that is the new emaxx 3905 diff gears, or the RCM 1/8 scale diff case and gears, but those are $100 each.