But why is the following an optimization (against my code)?:

It's an optimization against *my* code. You had a similar optimization already. (Your first elsif would have to be an if to be the same.)

Besides the 'redo' irritated me until I read in the docs that it doesn't redo do-blocks

redo, last and next only work on the various for/foreach blocks, while blocks and bare blocks. They don't work on non-loop blocks such as if, do, eval and sub blocks.