The FRS is an awesome car to drive.
The Miltek Manifold was never endorsed by Miltek themselves mate. They never fabricated one to sell, and is sold by Pumaspeed as a Miltek.
It has had constant cracking issues, which lead to expensive welding to repair. I'd steer clear of those matey.

Rob has loads of customers with sorted FRS's (like me) and could happily get you out in one if you need convincing.
Not mine though coz its off the road til March lol.