For what it's worth, I used to own the original Quad (57) and now I have the M4Turbo S (and also a pair of Apogee Stage full-range ribbons as a near-analogue of the Quads). Imagery-wise they are very similar; unlike box-speakers, which seem to have a degree of inbuilt (and spurious) depth, both the Quad and the Spatial Audio sound pancake-flat and two-dimensional on many 60s stereo recordings and extremely close on many others. This causes some listeners to conclude that they lack depth; au contraire, they have more real depth than any box speaker you care to name. Put on the right recording and it's difficult to credit what you're hearing; I recall playing Neil Young's "The Old Homestead" through the Quads and being transfixed by the way the "saw", which sounds like a theremin, was moving all over the room and seemingly going beyond the walls. Where I think the SA imagery is better than the Quad is that the instruments sound solid and tangible while through the Quad they sound ethereal and ghost-like.
Some may love the Quad's "delicacy", which to be honest, I think is exaggerated (live music doesn't just sound delicate) but the SA's can sound both delicate and awesomely powerful. And I'm sorry but the old Quads sound simply feeble on dance, techno, rock, or anything that needs weight, dynamics, and power to deliver the music. No doubt later Quads do somewhat better but I doubt if any come close to delivering what the SA's do in this area. They BLAST but at the same time remain remarkably controlled. The sense of snares being really HIT is the best I've heard from any speaker. And cymbals! The sense of metal being struck is again beyond anything I've heard. I do think they need to be WAY OUT in the room; I have mine at 7 to 8 feet from the wall behind, where they sound magical. At four feet out, they lose much of this entrancing quality and , honestly, I can't understand how anybody can evaluate them properly at three feet or even less. I don't rate them when placed like this.
Anyway, I can't offer a cast-iron guarantee that you'll prefer them to the Quads because they may sound too explicit and hard-core. if you prefer soft-core you may not get on with them. They are so direct and unvarnished.