Top Vent on Imperial Kamado

Is there a reason why they were made of heavy thick cast iron?
Designed to retain the heat better or?

Asking because I just scored an original IK #3 off Craigs and want to get familiar and see if its all that.

The included original pottery lid although cracked is still useable, but I bought a SS dog dish from Walmart and will attempt to fabricate my own cheap daisy wheel, lol.

Replies welcome! Thx

thanks.
can anyone suggest a makeshift heat deflector?
Don't want to spend the $ for one yet if I can use what is around the house.
Thinking screen splatter shield inches above lump topped with a water filled pie pan for juices?
Or maybe expanded metal cut to fit topped with foil?