Hi there. Geez, I had an account before and the ASR system couldn't locate it at all, so I had to make a new one just to answer your question.
I made a 2 hour drive back in 2018 to hear the Array 1400s that I ended up buying from the guy who listed them on Craigslist and it was worth it. Obviously I didn't bring any kind of T&M equipment with me, but I was able to use my own Hypex based DIY amplifier as well as the guy's McIntosh gear (not sure if it was tube or solid state) and I got to listen to the speakers directly next to a pair of these babies:
https://www.jblsynthesis.com/products/loudspeakers/type/floorstanding-loudspeakers/DD67000RW.html on the same source tracks using both my DAC and his (also forget what he had). I'm not kidding when I say I could barely hear any difference at the volume levels we used for testing and he also had a pair of Revel Ultima Salon 2s in the next room over on another set of McIntosh amps. The guy I'm talking about frequents these forums so it wouldn't surprise me if he chimes in. He had two pairs of the 1400s, keeping one and getting rid of the other.
At the time I had several sets of speakers at home including some JBL Studio 590s, JBL LS60s, Wharfedale Jade 3's w/ a subwoofer, some Elac Unifi UB51s, and a few odd pairs of B&W 600 series laying around. Nothing exactly high end, in other words, but the 1400s blew all of them away with my Hypex NC500 based amp and whatever DAC I had at the time. Might have been a P(o)S Audio top of the line DSD or a MyTek Brooklyn DAC+.
Anyway, the 1400s are great speakers in the right setup. None of the horn-Y-ness you might expect from their Dr. Seuss looks and giant vertically oriented waveguide w/ 3" compression driver tweeter topped by a 1" titanium super tweeter oriented horizontally in a smaller waveguide. Midrange on tracks like Waylon Jennings' album "Honkytonk Heroes" was absolutely amazing and the so-called soundstage was nice and deep. The high treble, for whatever frequencies I'm still able to hear (probably 13kHz) was crisp and realistic, so I believe JBL's claims that the supertweeter on the 1400s can reproduce close to 45kHz - like it matters in the real world). Bass is very punchy with a powerful amp and good room positioning, but I don't think they're super efficient speakers (87-88 dB/Wm or something). FWIW the room I had them in is relatively small without a lot of available space to bring the speakers in away from the walls (generally used a foot or less of spacing from back wall, but the port is in the back and the tweeter array is far forward already, so it wasn't a big deal - easy to move just a little closer to wall for better bass without any effect on imaging/sound staging). With clean amplification and a good source signal I basically couldn't get them to sound distorted at any volume level, to the point that my next door neighbor got my phone number to text me when it was too loud (and this was often for a while). I mainly listened to 80/s90s rock, Bluenote and acid jazz, hip hop, funk, and recent pop and electronic music (put on Daft Punk's "Get Lucky" if you end up going, sounds better on the 1400s than on any speaker I've ever heard <$5,000). I also tried the typical speaker test tracks that various hi-fi mags publish and they never disappointed. Never felt the need for a sub AT ALL, even in home theater applications.
To be honest, I loved the Studio 590s and hated most parts about the LS60s (very rolled off high end but damn good powerful bass "slam" lol). The Wharfedale Jades were great with tube based systems, but the woofers would fail if played hard w/o crossing over low bass to a sub (this is a known but not corporately admitted defect in that line - the cone and spider would separate from the tube surrounding the voice coil that they're normally glued to). But the 1400s were a game changer for me, and I had people over who have speakers ranging from electrostatics to high end B&Ws to high end Paradigms and with good source material they all liked the 1400s quite a bit. I never felt the need for any equalization (I do with the JBL 4349s I just bought - in part based on Amir's writeup and tests). The 3" aluminum CD and 1" supertweeter just meshed so well together in a way that the dual diaphragm 1 or 1.5" thing in these 4349s can't reproduce. Side note: that was a long thread with many people complaining about the dip in FR between 1.5 and 2kHz. I'm not sure if there's a measurement that can accurately portray the separation between instruments/sounds at all frequencies other than THD, but the 4349s are truly "reference class" monitors in that regard. The 1400s are just great too, but I hear things I've never heard on any of my acquaintances' systems *ever* on the 4349s and I'm more of a critical listener at times than someone who wants my system to sound - ahem - "musical" with "pace, rhythm and timing" lol. (both the 1400s and 4349s are excellent in that regard but the average audio nut would call the 4349s 'etched' and the 1400s 'musical').
Sorry about the novel, looks like I got carried away. Let me know if you have any specific questions. I'd say if you have a large-ish room, can place them in a manner that doesn't make the bass get boomy, they're in good shape and priced at $5500 or below, go give them a listen. You don't have much to lose at least auditioning them. If possible take your amp that you plan to use them with if the seller will let you; it'll be worth it. They are just OK with lower powered amps other than something like the Benchmark amp that Amir tested with exceedingly low distortion (I've auditioned it in the same system my 1400s were in); and they'll expose any weaknesses in lesser quality recordings pretty easily.
Word to the wise, JBL used this rubberized type material to finish the top of the woofer cabinet (but not the tweeter assembly/array) and it's very similar to that rubberized coating that BMW and a few other car mfg's were using for a while that is 1) easy as hell to scratch and 2) will decay into a sticky, melty gooey mess if exposed to sunlight and heat. Fingernails scratch them surprisingly easily. Take special care to inspect that top portion of the cabinets. I can recommend a product to keep that in good shape if you end up buying them, but I've seen plenty on the used market with really visible scuffs and degradation.
On that note, can I ask you what the asking price is, if they're in good shape and whether they have original boxes?
One last thing. You can still get a brand new pair in boxes for $7500, possibly less, if you negotiate with these guys:
https://homeaudiosound.com/product/jbl-array-1400-nibin-stock-7500/