I can't comment on the FAD, but not only just a few multi-BA in-ears are superior in terms of resolution and speed or control with really fast and complex tracks. I would say that it is better than
some double-BA in-ears, but
as long as they're not too shabby, most triple- and quad-BA in-ears will be (sometimes more and sometimes less obviously in some areas) superior when it is about bass speed (as long as the lows aren't boosted by too much and/or the BA woofers aren't back-vented), raw resolution and separation (the latter not always though). When it is about coherence, spatial persuasiveness, imaging, naturalness, authenticity and especially treble naturalness, the ER-4S is often somewhat better than multi-driver BA in-ears. Especially treble evenness and naturalness are things where the single-driver Ety is more realistic and even than many multi-driver in-ears.
Raw resolution is not everything, the overall package is probably more important and here is where the ER-4S excels - it doesn't do everything perfectly and isn't the best resolving in-ear but does so many things right - neutrality, soundstage, coherence, imaging, naturalness, authenticity, and resolution isn't bad by any means either.
As a single-driver BA in-ear though, it is very impressive what the ER-4S does - excellent extension, quite quick and arid bass, extremely coherent, very natural and authentic, round and realistic soundstage.
In the end, it still comes down to personal sound signature preference that is imho somewhat more important than absolute technical superiority.
And here, the ER-4S is the king (for
my preference and as an overall package for its price -
def. not the technically best from the in-ears I've bought, auditioned and reviewed but the most neutral according to my perception/possible HRTF and the diffuse-field target, and quite impressive what they got out of a single-BA in-ear that is on the market for over two decates).