Curious I downloaded and had a look at it. It does not generate Flash bytecode. It generates something it perhaps calls bytecode, then runs it through its virtual machine, in VirtualMachine.as, which is full of things like this:
//
//add v1 v2 %
//(add)
//v1+v2を%に代入
public function ADD (code:Array, pc:int) :*
{
code[code[pc+3]] = code[pc+1] + code[pc+2];
return pc+4;
}
It all looks pretty complete and well written, but if every time you do an operation it invokes a function which does several Array accesses it’s going to be an order of magnitude or two slower than the equivalent Actionscript code.