I have one and have used it without issue for the past two or three years. If you're using the stock alarm system and key FOB, then it's great. I never have to carry a garage door opener with me. Just press the second button on the key fob and the garage door goes up (or down).
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless