It seems like an easy solution. Put this zinc strip on your roof one time and you never have to worry about moss accumulation again. Do these zinc strips actually work? If you read the marketing the answer is yes, but reality is a bit different.

Zinc strips do help prevent some moss, but they aren't totally effective. The theory is that you attach the zinc strip to the peak of the roof and use rainwater running over the strip carry particles of zinc down the roof to kill existing moss and prevent future growth.

The picture below shows a zinc strip in real life. It's been in place for a few years and rain run off has been carrying zinc down the roof. As you can see, the top of the roof is fairly clear of moss growth but only for a few feet of roof surface. The zinc can't get all the way down the roof and moss is still growing on the bottom 2/3 of the shingles. 

So are they worth it? Probably not if you only put them at the peak of the roof. They only control moss for a short distance down the roof and don't prevent the need to clean the lower portion.  

You could put a strip at the peak, a second strip about 1/3 down the roof and a third strip 2/3 down. This would probably do a better job of moss control but it is a bit unsightly and putting nails through the shingles to attach the strip can lead to other water damage. 

I wouldn't recommend using zinc strips for moss control. The better option is a yearly cleaning of the roof with a broom and applying a moss control agent to the entire roof surface.