I'm not crazy about covering the radiator with another radiator. AR had a version that fit in the drivers side in front of the wheel, mirroring the other oil cooler. Not sure what happened to that.
I've got the VK oil cooler which looks the same as the Dinan and it's made a big difference v. stock, as has running higher octane on the track.
I don't run a tune and have not had issues with limp mode (although I suspect I'm running up against it most of the time).
I will do an upgraded radiator as soon as a little more reasonable option is available. That would be for greater margin + long term reliability (BMW radiators are notorious for crapping out).