The lesser known, more recent models from VJJB are the K5 and K6. Both are pretty much identical, with differences so mild that they are not worth getting too much into.
These earphones seem to have the same drivers as the old and good K4, but the are also cheaper - which might have something to do with their inferior tuning when compared to K4: even more bass (when K4 had more than enough of it), less mids (mainly crushed by the bass) and a more blatant V-shaped sound signature overall.
Not bad earphones, really, but at that price range there are better alternatives.
Good sound quality overall. The bass is ridiculously powerful, the mids are decent and the highs are comfortably tuned.
Insanely loud without requiring any amplification.
A superb design and use of materials (at least in 2016-2017 standards).
A great package, good looking carrying pouch and a decent variety of ear tips.
The mid-bass can overwhelm the mids sometimes.
Slightly edgy on the upper-mids, especially affecting female vocals.
It was difficult to keep a good seal with them, but your mileage may vary.
Incompatible with wide-bore ear tips due to narrow nozzles.
Package & Accessories
Ear Tips - Single-Flange:
S+M+L, grey (translucent), ?4mm bores
S+M+L, grey (translucent), ?5mm bores
Ear Tips - Foam:
Memory foam, black, ?4mm bores
Velour, grey, branded
Hook and loop fastener, generic
Build & Materials
Metal + wood, ?4mm nozzles, soft strain reliefs
Plastic (matte), single-button
Metal, soft strain relief
Silicone (grippy), 126cm, soft, bent
Metal, straight, short, soft strain relief
Comfort & Fit
I had troubles keeping a good seal for a long time with the included tips, probably due to the narrow nozzles. The best tips seemed to be the pre-applied foam tips.
Lows / Bass
Very extended bass response with massive mid-bass and sub-bass impact, as long as you maintain a proper seal. I was expecting these to be tuned more similarly to K4, but the bass here is even more emphasized, something that is not necessarily a desirable trait, as for many music genres (like punk/folk rock), the bass will just be too muddy and just overwhelming. But for electronic music - this bass is very well-performing without any distortions. Overall, a very fun-sounding bass, but surely not true to the original recording.
Mids / Vocals
Just like K4: The mids are warm, surrounding, energetic and very loud. Mostly neutral but could seem slightly darkened, especially on female vocals. Not superbly detailed, but still quite decent. The problem here arrises as a result from overwhelming bass response, that bleeds into the mids during heavy basslines, and especially muddies vocals. Upper-mids are a bit more edgy than K4, which adds slight edginess to vocals.
Highs / Treble
The highs are loud and crisp, sometimes might be slightly sibilant. They are somewhere between neutral and mildly darkish, but on the detail level - there isn't too much microdetail involved, just the usual highs you can hear mainly on V-shaped earphones. Not all that different to K4.