I have 41 eggs (mixed variety breeds-Easter Eggers, barred rock, Rhode Island, golden laced Wyandotte etc) in my genesis 1588 incubator at 15 days! I set 44 and have thrown out 1clear and 2 quitters. I'm doing it at school for my kindergarteners!- they're very excited! It's so much fun to candle...
Yes that is normal!! It just means they have pipped into the inner membrane and after awhile-(could be as long as 12-24 hrs) they will make an external pip! Good luck!!
The incubators I've used most are Hovabators. I have a Genesis 1588 and just got a 1602. The genesis is REALLY nice. The temp is factory preset and it has a digital reading. So far I've found it to be accurate. I really like mine.
The 1602 is little harder for me to get used to as I have to...