maybe a few comments on look and feel -- while most of these aspects have been mentioned before, it can't hurt to have another view, since subjective perception will vary:
I cannot comment on the probes, but maybe on some of your other observations, just to put them (and the SDS800X HD) into perspective for other potential buyers:
The fan is quite audible, but not terrible: Certainly louder than my SDG2000X function generator, but nowhere near the DHO1000 with its "ready for lift-off" fans. Probably on par with the old DS1000Z before I modified it years ago. In addition to the airflow sound, there is a bit of hum at ~200 Hz, which maybe a better fan could avoid. But it's not an unpleasant noise overall, and I don't feel compelled to do warranty-voiding modifications anytime soon.
I think the SDS824X HD is easily the most annoying instrument in my lab when it comes to audible noise, where there are also “big boys” sitting around, like the SDS6204 H12 Pro, which does have the potential to drown out the SDS824X HD, yet it doesn’t actually do this because of its temperature controlled fan.
In fact, I feel the SDS824X HD is even a tad noisier than the SDS1104X-E, which aligns well with your assessment of the SDS814X HD being about as noisy as the DS1000Z, which @Martin72 once measured some 7 dB louder than the SDS1004X-E, if I remember correctly.
In any case, I’m aways eager to turn off the SDS824X HD when it’s not in use, whereas the SDS2000X plus is already way more bearable. And then there are two instruments that I never turn off at all, because they are pretty much inaudible: then SDS2504X HD and my laptop computer.
[The screen is certainly bright enough, even with the morning sun earlier today; I have reduced the brightness to 90%. The DHO1000 was brighter though, I had turned that down to 60% or so. The screen's cover glass is less glossy than on the DHO1000, but not as matte as on the DS1000Z; I need to position the scope such that there is no direct reflection from the window behind me.
There we can see the actual subjectivity of these things: I’m content with just 50% LCD-brightness, but then again, my window is to the left of the instrument and myself.
The SDS824X HD screen is the glossiest one of all Siglent scopes by quite a margin. The SDS2000X HD and the SDS6204 H12 Pro screens are almost not reflective at all.
I like the user interface a lot! I have not actively used a Siglent scope before and am only beginning to explore all the functions -- but keep noticing details where obviously a lot of thought and refinement, based on practical use, has been put into the implementation.
Well, maybe it pays off that (other than some of the competition) Siglent decided to have consultants and beta testers from the industry for more than 8 years now. There was (and still is) a lot of progress all the time.
Since the SDS800X HD comes in the same housing as its non-touch predecessor, there are quite a few buttons! E.g. Decode, Acquire, Display have dedicated buttons to call up the respective menus, and there are also buttons to navigate recorded data. I like that so far; maybe I will use them less as I get more familiar with touch operation, but the buttons don't hurt. Their layout makes sense to me. I only wish Siglent had not opted for seven (!) different button shapes, which make the front panel look a bit more cluttered than necessary.
Well, the housing is a bit dated by now – after all it has been designed for a non-touch scope originally.
Have you noticed the “Quick Action” button? I have programmed it for “History”, because this how we can stop an ongoing acquisition and change to the history with a single button press – utterly convenient in my book.