Product review (5 stars): Works BETTER than expected!
I had an older, stainless steel/rubber stopper that never worked to keep the water from draining out -- you could hear it seeping out.  That stopper went "missing" during a kitchen remodel.  I spoke with an Insinkerator representative about some of the newer garbage disposals on the market -- if the stoppers really kept the water from leaking out of the sink.  He said "no, none of the stoppers are designed to totally stopper the sink".

I took a chance on this because of other favorable reviews, and I am glad I did!  I put water in the sink and left it overnight with no discernable loss of water.  So, I am keeping my older, working garbage disposal, ordered a replacement part for the mounting gasket, and am very happy to be able to use my sink as a stoppered sink!  I have no idea how long it will continue to work, but the price is reasonable therefore, I am happy with the product.