Originally Posted by philbaum 
I'm really thinking of getting one of these rubber hoods for my 300 as well. dosen't look like it may provide as much light protection as the hard plastic, but a lot easier to store.
You could block more stray light by going to a dedicated rubber tele hood such as a B&W 930.
A 3-way rubber hood (such as a Hama Tele-matic) would also block more light than the generic hood, but it takes longer to fully unfold and the filter thread is larger (e.g. the 67mm hood takes a 72mm filter) so you might want to carry an additional lens cap.