The main reason is I chose to have my manifold for yb made mainly for int as it's cheaper and easier to fit and you can keep the stock heat shield and tech only a small loss in top end power but the Efr with int gate has smaller housing so tech better spool.
The Evo I buy the manifold in and the main kit is base on ext but you can get int gate but needs a diff rad on Evo 7 plus so stayed with the known route.

Mark