I just sold a NIB OS .46 FX but kept my Thunder Tiger .46 Pro - mainly because of the needle valve. The OS has a remote NV which you can't rotate the orientation other than horizontal. I'd have to cut into the cowl of my trainer to accomodate the OS. The Thunder Tiger has a conventional carb mounted NV which is angled back and plenty far enough from the prop for safe operation - and NONE of us EVER reaches OVER the prop to make adjustments, do we?