What are your thoughts of the Comets vs. LZ A4 and maybe iSine 20? I've been looking at both as my next purchase.
That's a complex question, so I'll have to update this post over time. The iSINE 20 is in a completely different league than both of them, and with proper eq they sound like what I'd expect of a TOTL iem or really high end open headphone (the latter being the more fair comparison).
The A4 images better than comet (although separation is a wash), but it has a more traditional V-shaped signature. On Tom Petty's "Mary Jane's Last Dance" the A4's bass is more full and weighty but vocal presence is reduced vs comet. The comet's vocal presentation is perfect on this track with the vocals perfectly centered in the mix, not forward but not recessed. On the A4 the vocals sound slightly set back and thinner than comet, even a touch unnatural. With the blue front filter installed the A4 extends higher and has a more aggressive treble attack, leaving comet sounding smoother and more musical, but neither sounds harsh here. Overall I think the A4 eeks out a little more detail and edge at the expense of musicality with comet being the more danceable set. I prefer the comet's more unique tonality to the A4's V for this kind of music.
Turning to another genre, The Weeknd's "Party Monster" distinguishes the men from the boys when it comes to IEM mid-bass and punch. Comet performs surprisingly for a single BA IEM which one would expect to be unsatisfying for this track. It's not a basshead performance but manages to deliver an appropriate and even slightly indulgent amount of bass without crowding the mids. Meanwhile the signature T.A.E.C. lets the vocals and atmospheric production shine. Switching to the A4, I notice an immediate increase in stage size and treble extension. Vocals are less impaired than on the Petty track, and really don't stand out as better or worse than comet here. I expected bass to significantly outpace comet on this track, but it's really pretty close. A4 is slightly punchier and reaches a little deeper, but comet's subbass is tighter if less plentiful.
Really trying to drill down on bass, let's talk about Tycho's "Dream as Memory". A4 is at its best here. Bass is deep and punchy, highs are extended and airy, mids while slightly recessed add to the sense of stage in this case. Separation is excellent and the bass remains well controlled in the mix. This track proved an interesting test for comet. Coming back from A4, I immediately notice the less extended treble. It's not a PROBLEM per se, but it takes away a bit of the air that seems to envelop this track. Bass is polite and refined not but as in your face and present than on A4. This track on comet really illustrates the slight tradeoffs one makes when tuning a consistent all-rounder.
And besides that, Comet is a real gem in low-end segment… It's fun that when I wrote Russian Cascade's review few month ago, I've mentioned there that CA need some good entry level models, and bam, we've got Comet 
