I'm obviously responding to something that is rather old, but I can't help myself.
But it still needs the zoom crutch. Everyone can walk faster without a crutch.
What you call a "crutch", others clearly consider to be an advantage.
The scope decodes everything in the capture (subject to the limitations that were mentioned).
One capability that the Siglent approach has which other scopes might not have (and I can't say whether they have it or not. The Rigol DS-1054Z certainly doesn't) is to make it possible to place the trigger point outside of the captured area. From what I can tell, you can place the trigger point an arbitrary amount of time prior to the capture, and up to the right edge of the screen, which is the end of the capture buffer.
Also decoding only what is on screen gives you the problem that it is nearly impossible to correlate messages which may be in different parts of the acquisition memory. Get a Keysight or R&S scope on your bench and see how easy it is to be able to go through the entire record with timestamps relative to each packet.
In light of zoom mode, this deserves some explanation. Exactly what are you referring to here? What sort of correlation are you talking about? In the Siglent, cursors can be placed anywhere within the capture -- they aren't limited to the zoomed portion of the screen. This makes it possible to see the relative distance between any two portions of the capture.
Same for the automatic memory length. For the millionth time: limiting the memory size to the visible screen only is a serious productivity limitation. There is no arguing around that other than using yet another crutch (going back & forth between time/div settings). Everyone can walk faster without a crutch.
I'm sure it's a productivity limitation for some and a productivity enhancement for others. With the approach Siglent is taking, you
always know exactly what you're getting. There is absolutely no ambiguity, no guesswork involved, no off the cuff computation required. The time captured is the time represented by the screen, period.
There
is one disadvantage to Siglent's approach, and it can be a significant one: the mask test operates only on the full screen, and will not operate in zoom mode. This means that mask testing cannot be applied to a subset of the capture the way it is on other scopes, and this means you can't have it stop the scope upon failure and then examine some other portion of the waveform that is off-screen. This would be easy enough for Siglent to fix: they'd merely need to make it possible to define and operate the mask against the zoomed portion of the screen.
Remember I used to own an SDS2000 and the automatic memory selection annoyed the hell out of me.
Yeah, but you're used to using scopes that don't operate the way the Siglent does, right? How much of your annoyance is the result of what you're used to, versus the actual requirements of operating the scope?
Reasoning that none of the customers has asked for it is more indicative of the kind of customers Siglent has than automatic memory selection should be standard. Power users like me that need to have an oscilloscope which works efficiently will ask for it (or silently just don't buy the oscilloscopes from Siglent). Siglent has come a long way in the past few years and now they really have to start addressing the productivity issues (at least on the higher end models) in order to really compete with the A-brands.
I would argue that, at the very least, it should be an option -- make it possible for the user to choose whether to use the remaining memory for the automatic capture history or for the capture itself. Nothing in principle prevents Siglent from making both approaches possible.
In any case, save for the mask test issue, the approach Siglent has taken here is just different. It doesn't seem to be any worse or better as an objective matter (again, save for the mask test), only in terms of the specific use pattern that a given user brings to the table. In your case, your use pattern is such that Siglent's approach isn't the right one. But then, if zoom mode were your default use mode, that might change. Can't say on that.