The reason why you can find these modules is because 434MHz is an ISM band in some parts of ITU Region 1. You won't find an garage door opener there in the US. In the US you should use the 315MHz version which allows for license free use.

While 434MHz is in the 70cm amateur band you really should have an ID coming out of this thing when it transmits. All you need to do is shove your call sign out at 20wpm Morse code at the end of your transmission.

Otherwise it's a cool little hack.