I honestly don't know the answer to the nutritional value question.
One thing I wanted to clear up just in case there's confusion...
Carpets and boas will likely take chicks, mice, rats, whatever you put in front of them. So feeding them a varied diet is easier than it would be with a BP. With BPs, once they're on F/T rats it's best not to stray, cause they may not switch back easily if at all.
Not sure if that was already known, but figured it couldn't hurt to mention it.