Thats not true that its the only one that works!!! Ive had both the j's racing and mugen on my car and the j's racing is far superior to me!!! It all depends on your driving style!!!
I wouldn't agree with that either. There very much overrated in my opinion. Also very expensive. I've to changed from my j's racing intake to:
Standard Airbox
Spoon Carbon Kevlar Direct Airflow Pipe
Apex'i Drop In Panel Filter
Cold Air feed with Velocity Stack
And the car really feels much better and has way better throttle response. Im glad I changed my setup anyway. Anyway my point is I'd spend the mugen airbox money elsewhere but each to their own