My bantam eggs aren't really that much smaller...they still work well for cooking. The one exception are my bantam OEGB girls...their eggs are about the size of a quail egg! I crack those and let the chickens eat them.
We have 5 banty girls. I usually hard boil their eggs for salads or to pack in lunches. I actually have a customer who pays me $8 to make little deviled eggs. That's for a dozen eggs = to 24 little deviled eggs. Very time consuming, but definitely a party hit!
I just use them for eating as I would with any larger egg. Scrambled, fried, omlet, hard boiled...
The only thing I am unsure of is for baking, where it specifies a large egg...I would probably put 2 banty eggs in it's place.