And maybe Dave has a slight bias toward rigol
Not sure about a brand bias in general. But since Rigol puts a focus on being first to market, and on flashy user interfaces, their scopes might just make for the more "exciting" video content, which suits Dave's style and audience better.
His DHO800 video could talk about "first 12 bit scope for everybody", shiny GUI, new form factor, VESA mount, USB-C power supply etc.; all pretty catchy and visual topics. An SDS800X HD video would have to focus on "another 12 bit scope, but better", talk about FFT and other analysis capabilities in some detail to explain the differences, while the form factor and appearance are "basically the same as the predecessor, now in black". Very relevant for the audience in this forum section, but not a very impactful video for Dave's channel maybe?
There are 800 comments in this thread, there is clearly an audience for a review.
Also it's 3 scopes, so it's an exciting time, could be quite a bit of content to compare all these to each other and to the Rigols.
Or maybe he is preoccupied selling BTC.
Dave is in Youtube business. If it ain't flashy, loud, or controversial, "groundbreaking", "game changer" and all other stuff like that, it is not worth of a video.
800 comments here by altogether 30 people does not buy bread on Youtube.
We could argue if he ever did a real "technical review".
Dave does some presentations of products, some features and that is it. Biggest thing is if he finds a bug that can be made into bombastic title.
Not a critique of a Dave, mind you. That is the media he produces for. He didn't make the rules.
Perfoma01 does reviews. And his single review produces a 100 pages book.
Rudi made some reviews of scopes, it ended up in 3-4 hours of material across half a dozen videos...
And nobody cared. Because it looked too much like a real work.
Not entertrainment. That is what Youtube is all about.