Apparently the 900 series Bode function is a bad joke!! Rigol has had plenty of time to get this right as Siglent set the bar long ago for lower mid-level DSOs. Siglent learned from tier 1 folks like R&S, KS, LeCroy & Tek, and implemented a nice Bode function, albeit slow, but quite functional.....and they are "listening" to users an apparently will introduce a new version addressing some of the limitations (hints by some folks with early versions)!!
The 814 we have has an FFT implementation that's not applicable for professional use, nothing close to Siglent's. Suspect the 900 series has the same FFT as the 814 we have, if so then wouldn't bank on Rigol getting this right anytime soon, same as Bode Function.
The 814 is a really good basic DSO implementation, superb hardware & build, attractive form factor, good UI, nice HW features, and very good value IMO as a basic DSO. Most folks reporting haven't discovered any serious issues with the 800 series.
However, the 900 series seems riddled with issues, mostly related to the "expansion" from the 800 series, and not hardware related. This is likely the target for the upcoming Siglent SDS1000X HD, as Rigol hit a home run with the 800 series, but fouled out with the 900 series.
Without a custom ADC chip set, Siglent can't compete with the 800 series, so wisely focused on the higher price 900 series & market segment, and with the apparent issues with the 900, seems Rigol has left the door open.
Not surprised that some of the 900s are being returned, with what's been shown, we would have also done so. With the upcoming SDS1000X HD, expected polished performance like intro of the SDS2000X+, suspect the market for the 900 series will quickly shift away, especially if Siglent prices the HD within reasonable range of the 900 series.
We would have our own DHO814 if not for the upcoming SDS1000X HD, but may still get one since it's just a darn good little DSO in a small, stylish well build package, that's very reasonable and performs quite well as a basic DSO.
As mentioned we consider the DHO800 as the equivalent of a handheld DMM, and the larger more capable MSOs as Benchtop DMMs, gotta find an
excuse,
need,
plan, requirement to have both
Best,