I now have 5 days experience with the large Premeir heat plate and my first batch of chicks ever (25). I love the heat plate, especially at night. They all go to bed (they go quietly if I gradually reduce the light until it is dark) and don't make a peep all night.
I have read this entire thread, and see the logic of mimicing a mother hen - i.e., the temps outside the heat plate can be quite cool and the chicks just go back under the plate when they need to warm up. But, I have a question about that. If I don't have a heat lamp on, the chicks spend much more time under the heat plate and only about 1/4 to 1/3 of them will be out eating and drinking at a time. This is even at 60+ degrees in the garage in mid-day. I've experimented with long periods without the heat lamp to make sure they were not just taking a quick nap. If I have the heat lamp on and it is above 80 degrees in the brooder - most are out eating, pecking, running around and only a few will be taking a rest at any given time. So, I am basically able to control their level of eating and activity, it appears, by how much I run the heat lamp (also the light at night, of course).
So, is it better for them to have the supplemental heat, even though they can handle the cooler temps with use of the heat plate? It would seem they would grow faster with the heat lamp. And should I extend their day length with a lamp or mimic the actual day length? They have been putting in a full 10-11 hours of sleep without a light each night. That is another reason I hate to see them retiring to the heat plate a lot during the day. But, we kind of lose the energy savings (during the day, at least), since I have the heat lamp on much of the time.