I was thinking of adding one of these to my rig with the thought that I would output it to a tv for previewing my projects.
Is there any advantage to this over the video card hdmi output? I was hoping that it would allow me to preview in realtime without any slow down of the workflow.
The Blackmagic cards and other I/O cards give a raw video output which means the color space is not effected by the OS and video driver. It's a direct color space output from the application to the monitor. That is why they are used versus video cards for full screen monitoring/grading. Video cards can potentially output the same colorspace information but they have to be configured ie calibrated to do so via the OS, driver, and or colorimeter and software. It's more complicated but still doable. The easy answer though is get the Blackmagic card.