Others say...

"Not good for Aviation Spotting."
I have a Canon 100-400L IS and this filter works good but I use this lens mostly for Aviation Spotting and the problem that I have is that when any light from the airplane like the landing gear lights are on, I'll get some very nasty reflections so I don't recommend this for this particular activity.

"ok, but you may be better off with no filter at all"
if you're using a hood for your lens, you probably don't need a UV filter, but if you shoot a lot without a hood, this might be a good option.

"Love it! Does the job, go with Canon! Don't go without one!"
I try to buy Canon whenever it's available, or whatever UV lens filter that gets paired with the lens I'm buying on Amazon's "Most Frequently Bought Together" feature.

I installed this on my Canon 24-70mm f/2.8L lens right when I got it--luckily, this was shipped and arrived before the lens, because if you're like me, you like to play with your new toys the day that you get them. Had this not arrived, I would have shot for hours and hundreds of pictures without a filter protecting the front element of my new lens.

I'm relatively new to photography (1 year), and all of my friends have always told me to get a UV filter--not so much for the UV or Haze, but for protecting your lens from dust, scratches, bumps, etc. You can comfortably wipe and clean this lens filter with your T-shirt or whatever cloth, napkin, paper towel, your fingers, etc and still have piece of mind (that is, if a lens cleaning cloth or micro-fiber cloth isn't available and there is dirt/dust obstructing the front).

It was explained to me this way--if I can afford spending hundreds to thousands of dollars on a lens, why would I be so cheap as to not buy the most basic protective equipment for my lens? One small scratch on your expensive lens, and it will be rendered completely useless.

Bonus--this lens also fits the lens cap, so no worries about that. The only thing I have against this product, but more specifically any product sold on Amazon, is the price fluctuations--even from one day to the next. I'd appreciate much more if Amazon always sells at the lowest prices. I got it for $26.21, so if you're not in a hurry, you can always wait till the price drops a bit before buying this.

"a little bit heavy"
This filter is good, but a little bit heavy. If you willing to spend a little bit more money on the filter, and willing to have a lighter one. Then don't pick this filter. However, it built with metal, so you can feel the quality. Weight seems like the only problem I have. With this price, I think it's worth it.

"Previous Canon Filters Worked OK"
I have used this filter on previous cameras/lenses satisfactorily. This one arrived loose in the box, outside of the case and was damaged in shipping so returned it to Amazon. I have noticed that the last few shipments from Amazon have been poorly packed.