NDI is free. It also requires wired gigabit connection, and can have some quirks when trying to use it with certain games (due to GPU prioritization). It does let you get around the problem of wanting to run your monitor at a high refresh rate but only capture at 60fps.
On the other hand, a capture card costs money, and requires extra cables run. But, it has absolutely no impact on your gaming PC, and should capture exactly what is being output regardless of what is running. But, it does come with the caveat that your gaming monitor needs to be running at a resolution/framerate that the capture card supports (which in the case of the HD60 pro, means a max of 1080p60).