Product review (4 stars): two o-rings!
Product has two o-rings and so far no leaking. I did run the water through for a few minutes as instructed and all the air pockets seem to have been worked out. At half the price of the name-brand item, I'm pretty pleased. Now that I know the item has the two o-rings we will probably spring for the 3-pack to get a better deal next time around.