You can also get clear vinyl wrap for stone protection but with the complex shape of the MGF bumper you would certainly need someone who knows what he/she is doing to apply it and it would cost a lot more than the Plastidip. I have done a Trophy rear spoiler in vinyl and it's not as simple as the Youtube videos make you think!
My concerm with the clear Plastidip is the quality of finish you would get. You would have to be very careful to avoid dust or an orange peel finish as they would just make it look like a bad paint job.