Per YT :
Kerak Telor can be translated literally as "egg crust". Kerak Telor is a combination of rice, chicken/duck eggs, dried shrimp, grated coconut and some spices. When we ordered one, the seller asked us how many eggs we wanted. Actually, there is only one type of kerak telor. What makes is different is only about the egg (chicken or ducks), and how many eggs we want to have. At least this what we understand.
If you order kerak telor using duck egg, it will be more expensive. Also, if you want to have two eggs, it is a little bit expensive (than having only an egg). Two eggs mean bigger size, more rice, more ingredients.