Kdenlive is my program of choice to make awesome movies and using the green screen effect on my videos. The reason why I love Kdenlive is because its free, intuitive and works well. Yes it crashes quite often but it has that automatic recovery feature so you never end up losing any of your progress even if you forgot to save (as long as you saved at least once). I have tried Magix Video pro, it costs 400$ and it seems to crash even more! So I went back to Kdenlive.