They have trouble tuning them. Not many tuners know how to tune the new throttlebodies. None of them are junk but they really aren't needed unless your are supercharged and trying for 600 rwhp. The stock one becomes a restriction at 550 rwhp, so most people don't really need one for the head ache.
As stated before, throttle body is more of a headache than not unless you're in the extreme horsepower range. I am having absolutely no issues with mine being a restriction at the 448RWHP mark. The money can best be spent elsewhere on your vehicle.