Well for one, they actually practice clockwork magic stuff there! Only smiths are permitted to enter the ring, as the dwarves practice their secret crafts there. There is stuff that will be in the Ring that not even the Cothromach dwarves will have been practicing. Leo may need to pull some strings to learn extra stuff (Gendry was granted permission to learn clockwork magic via a boon), but Leo would otherwise be learning among the best of the best.