Hardware Recommendation

I'm looking into starting to play around with capturing HDMI streams (4k and 1080p); currently for later uploading to Youtube, but not for live streaming. I have a Linux server here with a couple of VMs that I might want to try using for capturing (not sure how well this will work without GPU access). If it shouldn't work out, I can fall back to Windows 10 on some desktop.

What I'm currently trying to figure out is which hardware best to use to capture. Given that I may want to change the PC meant to capture, I guess an USB device would be handier than a PCIe card. Alternatively, I have seen that Bird-Dog is offering a Flex device that turns streams into NDI streams. That seems pretty flexible as well, as I should be able to pick up the NDI stream with OBS on changing machines.

Anyone having a view/recommendation on what would be better to capture streams, USB (AVermedia Live Gamer Ultra, Elgato Cam Link 4k, ClonerAlliance Flint 4KP Plus) or a Bird-Dog Flex 4k? Any noticeable differences in quality? Any issues in support under Linux, or stability?