...I am, however, looking for a bit of a change, and I figured that the ZMF Verite Open or Atrium might be a nice alternative, without sacrificing too much in terms of a solid tonality... The other alternative would be to maybe stick to what I know, in the sense of chasing an OG Utopia instead.
's advice is spot on. I can add a few additional points as I had the Clear for a couple of years and at the same time as the Vérité. I've also heard the Utopia and the Atrium in my system, each for more than a week.
(For reference, my gear consisted of such DACs as the Bifrost 2 and Gungnir A2 multibit and, for amps, the Stratus, Phonitor X, Mjolnir 1, SW51+ and Massdrop Cavalli Tube Hybrid. My Vérité have the Universe pads.)
I wanted to upgrade from the Clear to a pair of headphones with better resolution and staging. I opted for the Vérité as it kept the Clear's punchiness and versatility and because the changes in tonality were appealing to me. The Vérité has better bass, as in it's more robust, possibly deeper, but also more textured and tonally rich. The slightly laid back tuning was also appealing, and while I found the treble to be a bit crystalline and hard at times on the Clear (this was amp dependent), this wasn't an issue for the Vérité, although the Vérité was more fatiguing for me with the wrong amps than the Clear. I'm sensitive to too much emphasis in the upper mids and lower treble. Warmer DACs and amps worked better for me with the Vérité than the Clear - again, for my preferences.
The Vérité also shares many similar qualities with the Clear - the incisive, snappy attack in the transient response, although the Vérité has better, more lingering decay (I think, this could be a faulty recollection), and something of the clean, clear almost transparent presentation. There's more warmth to the Vérité but it's not an especially colored sound, whereas the Atrium does have a warmer, more analogue and colored but less pristine, clear, and snappy sound. The Atrium's leading edges (i.e. attacks) are more rounded and softer, and the Atrium, while plenty resolving, is significantly less so than the Vérité or the Utopia. The Vérité and Clear trade blows for imaging but the Vérité has better layering and separation, it doesn't suffer from the microscopic presentation, and it offers much more of a sense of openness and spaciousness.
In terms of resolution, the Vérité is a significant step up from the Clear. It quickly became apparent to me that the Vérité is a totl headphone in comparison to the Clear. The same can be said, of course, for the Utopia. The Utopia does indeed share many of the same qualities as the Clear, again with superior technicalities like resolution. The Utopia's bass isn't as robust as the Clear's (or the Vérité's). As a result, the Utopia has more of a kind of reference/neutral presentation. It's quite punchy but less so than the Clear, at least from memory. Please note that I didn't have the Clear and Utopia at the same time, so this is going off memory. The Utopia has a slightly more open and spacious soundstage than the Clear but it's still closer to the Clear than it is to the Vérité, which is significantly more spacious.
I can't add much of value to what @johnnypaddock
wrote about the Atrium except to say that it has a decent amount of emphasis in the upper mids/lower treble (where, exactly, I'm not sure), which meant that I preferred its tuning with the solid mesh and the Universe pads, which made for a darker tuning. You do have the options of pad and mesh rolling, which could dial in the tuning closer to your preferences, but the Atrium does have a more markedly different sound to the Clear than do the Vérité or the Utopia.
Since you're buying used, I'd suggest getting both the Vérité and the Utopia and then selling which ever you like the least. Good luck!