No, I've never heard of them and why wouldn't you just call this thread "Decline Hamstring Extensions?" or something along those lines? You may have gotten more replies.
Anyways, you need to move the big weight to make big muscle. IE: compound lifts (squats, deadlifts, good mornings, cleans (and variations of each). You also need to eat in a caloric surplus with a high protein intake. You also need to sleep well as well as have a properly planned exercise routine with volume and rest management and proper deload intervals...etc etc etc.
So saying "exercise X gives you huge legs" is pretty much a total misconception.