This author has no plans ever to try to evaluate capacitors again. To undertake this task properly is more time consuming than any other previous review activity. Most of what has been written on this subject elsewhere has been based on single experience of capacitor substitution in just one context. Only Ben Duncan and Martin Colloms in HiFi News and Bateman in Wireles World stand out as attempting academic rigour, which becomes easily explicable as soon as such an exercise is attempted. Inevitably visual analogies abound, because we are a species whose sentient data is dominated by the visual and therefore our language reflects this. Reflections may be audible or visible, but thess reflections will be metaphorical.
The Cicada Copper capacitors are definitely preferred over the aluminium versions in critical positions, but the aluminium are available in a wider range of values. They are all MUCH BIGGER than most competitors, and the copper are slightly bigger than the aluminium.
To summarise, in series applications (coupling caps), their character is somewhere between Hovland Musicap or Infinicaps (indeed, similar character to MCAPS), but with greater clarity, and the better types of paper in oil (old school Audio Note copper foil), regardless of circuit voltages (something of a surprise). The Mundorf MCAP connection is obvious in the aluminium foil Cicada voicing and the copper foil versions go that bit better. Frankly these differences are tiny in the great scheme of a whole audio system (they would have seemed bigger in a single A-B test against a singkle reference) but would affect a low component count project more than a complicated circuit. A single valve line stage would foreground these differences, while a sophisticated class AB bipolar transistor amplifier would mask them completely. Anyone considering building an SET or the Raven or an Allen Wright FVP project, might notice the difference.
In power supply bypass, cathode bypass or local PS decoupling they are not sufficiently better than some less expensive types, and while a proprietary electrolytic bypassed by a CIcada is not as good as a Cerafine or Black Gate alone, a shunt stack topped of with a little silver mica or Cicada aluminium serves well enough for most applications. The less expensive Aluminium foil types are indistinguishable from copper in power supply bypass postions and neither are much better than much cheaper types here.
You'll notice that there are some comparisons here between the Cicada capacitors with legendary capacitors that are no longer available new; to be compared with such company is high praise indeed, but also keeps some of the myths in perspective. Old capacitors are not works of art, they are just old capacitors, with all the risks attached to any old engineering component. However, there are also the risks in a market that behaves like the art market, that things are not always what they purport to be. Brand new reputable supplies will always be a safer bet than NOS (New Old Stock), but the lack of retail price information renders value judgements impossible.