Decimator MD-HX - Scaling Output

Have me an Atomos NinjaII and Ninja Blade that worked pretty ok for some years..
However with the purchase of a pair of smaller Canon RF800 cameras to use as static shots, i realized that they can only output 1080p60.

I'm working on the BMD ATEM 1 M/E
And my ninjas were not picking up the feed, then i realized that they can do up to 1080i60..

So to get me working, i got me the Red Box decimator MD-HX

Got it working good conversion from 1080p59.94 to 1080i59.94 and the Ninja's are seeing the video..

How ever i see a HDMI TYPE Setting:
HDMI RGB 4:4:4 and
HDMI YCbCr 4:4:4

which of these should i be using?
What's the difference ?

Thanks