I have tried giveaways, but the quality of the leads you get from them is very low, and, nowadays, there are so many of them that the actual number of leads that you obtain is usually very very low.
Some of the giveaways where I have taken part recently, the number of contributors has outnumbered the number of visitors to the giveaway!
I did take part in a couple of "group giveaways", where there were only 10 contributors and we all emailed our lists about the "group giveaway". That worked well for me.