I've been looking into DIY methods for a month or so now, and from what I'm understanding is that you really don't need something that passes all the standard through.
From what I've read in the Amazon reviews, this splitter will carry HDR when split/downgraded.
HDFury does not as far as I know; I bought this one on Amazon that works fine. I had some trouble with it that's well-documented in the product reviews, but they can be avoided if you make sure you are using HDMI cables with the appropriate AWG rating for the cable length.
In terms of the HDMI to CVBS 4K scaler, if you don't already have it I would not use it. There's no benefit to using that versus whatever came with your Lightberry. IIRC the 4K scaler is a separate purchase for $100 or more. The HDFury Linker is downscaling the signal to 1080p (or lower) for you to process so you don't need a second downscaler from Lightberry.
Your post is a little old, but I thought I'd reply - I ordered lightberry last week and just ordered their Lightberry HD kit and their video grabber. Then I ordered on Ebay the same 4k HDMI to AV converter they offer and a 4k HDMI splitter from Amazon that supports HDMI 2.0. Here is the link to the splitter: https://www.amazon.com/dp/B01FSFV4X8/ref=twister_B01FSFV2V2?_encoding=UTF8&psc=1
The last two items are coming from China, so I'm just waiting for those to arrive - hopefully it all works! Have you found any other solutions?
It's not the 4K that's the problem, it's the HDCP 2.2 copy protection that is, which blocks it from working with non HDCP 2.2 and HDMI 2.0 sources. That being said, I think I've found a solution in a piece of hardware that is supposed to strip HDCP from the signal:
I'm still waiting on my Lightberry, so if I can actually get that to work, I'll make a post here.