Unfortunately, the flockraiser is a crumble which is the big drawback...lots more waste, and it's a little more expensive than the layena (both reasons are why I mix the two). I usually make the switch around 12 weeks. Alot of people will say that's too soon, but it's a convenience thing for me. I don't have enough room to pen practically full grown "chicks" seperate from the others, so I have a layer pen that gets the combo (pullets go in there around 18 weeks) and then there are two adolescent pens that get fed the flockraiser exclusively. the pens I keep my babies in are too small to house chickens older than 10-12 weeks for very long, so it's a trade-off.