Hi, Regel,
Sorry for the delay.
As far as a run-and-gun recorder, I find my D100 a bit too large to carry around all the time - I normally have a Sony PCM-M10 in my pocket (and a pair of Luhd binaurals hanging around my neck), or my trusty Olympus LS-11. I would also find the LS-100 too large, but if you don't, then great - you'll also find the D100 very comfortable in use.
Noe, the recording sample. The seller has wisely left enough silences in-between - and I fail to hear any self/noise above what you might expect from the D100. (Is that the Nagra "green mic").
I do miss some low-end (the D100 is great at that), and I agree that there must be a highpass involved. Otherwise, we would have heard some pops (at times, he's speaking too close to the mic), and rumble (the Nagra is not in a shockmount, but I reckon on a table which gets banged on a couple of occasions).
The D100 would have given a slightly brighter top-end, and, if no highpass is involved, more low-end, but, judging from this sample, noise floors are very similar.
Where you will find a major difference with the D100 iw in soundstage. With its mics set to the pseudo-ORTF position, the D100 presents a fantastic, wide soundstage - the set of mics for the Nagra SD seem to offer essentially mono sound. So that makes the Nagra great as a "sound notebook", and great for dialogue or sound effects, but not good for, say, a mid-sized orchestra, a dawn chorus, etc.
(Then again, for such a recording, you are likely to use your "big iron" - the MixPre6, your DPAs, etc. So it's all a trade-off, really.)
And, without a Nagra SD at hand, and no experience with it (handling, user interface, battery life, etc.), so I think someone with more experience should chime in.
Oh, and Happy New Year!