... they've actually produced some quality, decently-documented, and reasonably well-supported goods.
i'm sure they did, like DP832?
The slight difference in specs
slight? that's 7dB difference, and hell, this is what one-hung-low wrote on their datasheet, who knows how they perform in real.
I remember you being quite favorable about the RuiFeng chips when they were discovered in the Owon DSOs - I could post your messages about them to refresh your memory, if you like
sure, do it, if you have nothing else to do. The fact that a cheap single-chip ADC (with embedded interleaving) is better than 8-10pcs external inerleaved and overclocked ADCs - at same price - didn't make anything bad in my statement. But when you compare these RuiFeng to others in same design class, then you will see how much worse they are. At the time as Owon started to use them, i've even ordered samples from RuiFeng (and finally got nothing because nobody was able to deliver only few ICs, i'm not an idiot to buy 100pcs to run a test with few^^).
Do you have confirmation from an unimpeachable source that this is, in fact, what has happened?
unimpeachable source? sure,
I told you already here how to confirm that:
https://www.eevblog.com/forum/blog/eevblog-360-rigol-ds2000-oscilloscope-teardown/msg252800/#msg252800Personally, if the specs of the DSO (NOT just the ADC) in question are good
These specs you talking about are piece of marketing paper, i'm talking about controlled specs of one-of-the major DSO parts.
I simply do trust National/TI more than Rui-Feng.
Personally, if the specs of the DSO (NOT just the ADC) in question are good - as a long-term owner, I'd prefer to have the one WITHOUT the overclocked ADCs.
as a typical long-term-oriented owner i started years ago collective order to be prepared for replacement of "all these broken AD9288 in the future". Finally, after 4 years only few failed (on all who used them, sp Instek, Tekway and Rigol). Later i've recognized that one can perfectly overlock newer batches of AD9288-40 to AD9288-125 with almost no performance loss (i've tested with older non-rohs ICs and was not able to overlock that stable and that high as with new rohs chips). Actually Instek was the first company who used overclocking on these ADC, so i'm sure they know what they did to ADC08D500 on their latest DSOs. Now depends on how long one wish to use a particular DSO, when only max 3 years, then gosh, who cares about bit more heat and bit bigger fan? But for sure, when one wish to have stable gear, for maybe more than 3yrs, then for sure don't buy Instek. In regards of ADC08D500 vs. ADC08D1020, only National/TI knows if there is real difference, from their app notes and datasheets (not fixed since months and lot of emails, it seems that nobody cares on nobody knows really what inside these ADCs) i would say Instek know what they doing. I prefer however a gear that could run "forever".
But for now we can only speculate what ADC Siglent is really using, looking on price it is perfectly possible to get ADC08D1020.
They are similar or only I feel so.
of course they similar, once one chinese manufacturer recognized that "this can be done cheap" all copying the idea. However, Rigol designed already years ago similar thing - the DS1000CA series (two FPGAs, fast single IC ADC, "high" wfms rate), but the high price was show-stopper for many users. The DS1000E was in principle step backwards to satisfy management. ATTEN copied of course that "dual-FPGA" design as well, but shortly after release stopped sales of that model due no-revenue as well. There is nothing new, others (e.g. Tektronix) using similar designs since 15years, it was only question of time until low-end manufacturers would be able to use that technology as well in <1k USD gears.
This is billion of dollar market (in china only), so one have to be competitive all the time. These new designs are absolutely "need", you can't (sorry Hantek, but you guys are really saving money on wrong side with MSO5074FG) simply add 2 extra channels and signal generator/LA and hope to "make still money". When other can do xxxxx wfms/s, you have to do as well, and same for other features. Sure, Rigol shot competitors with DS2000 series (not that DS4/6 are bad, but that's different price sector), but as we can see UNI-T, Instek and now Siglent managed to design good DSO/MSOs as well (as far one can tell from paper, i still didn't saw any real performance test of UNI-T, about Instek we knows that it does perfrom sufficient to be in same class as Rigol). Now it is not only "billions" of wfms/s, but as well other features are important. For us, endusers, it is of course good to see all the new gears.
When checkin the history it was clear that Sgilent will compile good set of features, Rigol DS2k - intensity grading and high wfms UNI-T higher wfms, Instek color grading, Siglent 256 level color intensity grading. Same for other features, more and more for same money. I only hope things like on DP832 will not be copied by others as well, i don't mind to pay few bucks more and get stable gear.