They're great if you like breakin' axle shafts. Most MOAs are Bergs. I think folks like them because the are really light. Your average Berg MOA will weigh in at around 6lbs where the average Bully (alloys) will tip the scales at 7+lbs. All I can say is that I've seen alot of berg breakage.
Here is a review thread for Berg's new V2 rolling chassis. I saw this thing up close and it is pretty cool.
http://www.rccrawler.com/forum/showthread.php?t=206560