As I said, the block form does add a little overhead, because it creates a lexical scope. It's very minor though, so it's generally better to go with whatever you think is more readable.
When you need to micro-optimize a tight loop that gets called millions or billions of times... that's when you start looking at removing unnecessary lexical scopes! The block forms of grep and map can be replaced with the expression forms; if/elsif/else chains can become ternary operator expressions; foreach blocks become statement modifiers; etc.
use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name
