Shadowplay has a limit of 20 minutes if using "Shadow" mode, but it's "limited" by your HDD space if you use the "manual" mode.

It shows great results, without compromising your gameplay, however :

1- You need AT LEAST GeForce GTX 6xx card
2- You MUST play in fullscreen

But if you fulfill those requirement, it's free, powerful, easy to use, and convenient. I really like it.