PS: I am willing to discuss any error I made in my conclusions. I am just a human
no i think as you correctly point out - the relationship between the quoted nominal inpuut (analog) bandwidth versus the sampling rate is indeed somewhat fungible matter. not least because on the analog side the nominal bandwidth is the -3db or half power point (or 1/rt2 whatever it is). so a higher analog bandwidth would reduce that attenuation level at the upper end of the total usable frequency range.
and also as you point out - that other factors such as the resolution, or the accuracy (of the adc), or the time wise jitter. things like this can differently impact the resultant noise or confidence onto specific waveform types, or specific measurement types. whether it is some fft analysis (or bode), or the whole multi sampling / repeating waveform analysis.
so that all makes sense. but what i am seeing here is also that there is this camp of people making the 10x generalization (broadly across purposes). and theres the people quoting the nyquist 2x upper aliasing limit (for some sine wave or whatever). then i suppose the 6x is meant to be a sorta 'in-between' those 2 extremes perhaps?
so looking here at the 312ms/s for the industry std analog -3db attenuation bandwidth... that is how much? ---> about 50mhz for a 6x factor? is that a reasonable working generalization for 4 channels?
ah but if we need only 2 ch then its 100mhz. that is what another guy has already said here earlier on in the thread. (to maintain that 6x factor). i believe these are fair assessments.
but a nicer assessment will be after proper reviews with the supplied probes, and a costing breakdowns, for the 800 versus 900 choosing. and those other included features too. because that also feeds into the overall value proposition. for the total sticker price.
as a false advertising - yes i agree its disingenuous claims. but also that it 'doesnt hurt' so long as you understand the truth. rather that instead the 900 seems worse value doe to being priced too much higher than it idealls should be nearer to 800 series somewhere inbetween.