[ProfessorBuzz]

There's really no downside to having it if you have the cash.

One thing I dislike about some of the Sigma filters I own is the box is awkward in the field, and they tend to have thick frames. Not an issue on the 150-450, but a real issue on wide lenses.

[Sakura]

Other than the 99.76% transmittance, there was no mention of coatings (well, there was mention of a water repellent coating) so from the description, we don't know anything about the reflectivity of its surfaces, and those can be the killers for anything you put in the light path (and certainly makes the case for those who prefer nothing in the light path in front of the lens). Personally, I would go for a super-multicoated UV filter for lens protection, although it won't offer the super hardness advertised for this lens accessory, but may be the better optical choice. That's just my opinion but as mentioned, you have to choose for yourself.

That was indeed my initial question, not about the need of a filter, but of the experiences with this filter. Just as you mentioned, there is not much to find about this filter other then what Sigma want to tell us.

I know that using any filter could effect the picture quality and give extra reflections.

So it seems no one here has experiences with this filter yet (or hasn't reacted here yet)