General information for folks that might be interested in the condensation complaints relating to the S12 but the same applies to any metal shell IEM, some may have never come across this or considered it, I know I hadn't until several years ago when I tried IEM for the first time.
Some simple facts to consider when deciding between IEM options:
IEM are typically made with metal, resin or plastic shells.
Metal absorbs cold and tends to hold the cold quite well. Cold materials will form condensation when in a warm humid environment, our ears are warm and humid, that is inescapable physics.
Plastics and resins won't absorb and hold the cold as readily so won't form condensation as readily but still could if subject to a sufficiently cold environment.
Metal shells are stronger than resin or plastic, especially resin which is actually quite easy to break. I have broken two sets of resin shell IEM intentionally and some folks might be surprised how thin and weak the shells can be, you would not want to handle them roughly or get unlucky and drop them from a height onto a hard surface like a tiled floor for example.
If you want or need strong shells you buy metal and accept the limitations that come with that.
If you don't want condensation to occur because you live in a climate that this might be a factor you buy resin or plastic and accept a different set of limitations.
Luckily there are plenty of good sounding IEM at various price points so there is something to please everyone if we make a selection with an understanding of the physics behind the material used in manufacture.
Some simple facts to consider when deciding between IEM options:
IEM are typically made with metal, resin or plastic shells.
Metal absorbs cold and tends to hold the cold quite well. Cold materials will form condensation when in a warm humid environment, our ears are warm and humid, that is inescapable physics.
Plastics and resins won't absorb and hold the cold as readily so won't form condensation as readily but still could if subject to a sufficiently cold environment.
Metal shells are stronger than resin or plastic, especially resin which is actually quite easy to break. I have broken two sets of resin shell IEM intentionally and some folks might be surprised how thin and weak the shells can be, you would not want to handle them roughly or get unlucky and drop them from a height onto a hard surface like a tiled floor for example.
If you want or need strong shells you buy metal and accept the limitations that come with that.
If you don't want condensation to occur because you live in a climate that this might be a factor you buy resin or plastic and accept a different set of limitations.
Luckily there are plenty of good sounding IEM at various price points so there is something to please everyone if we make a selection with an understanding of the physics behind the material used in manufacture.
Maybe this will help avoid the formation of condensation on the sound tube grille? The advantage of this solution is that most of the body remains made of metal, and plastic sound tubes do not spoil the appearance in any way simply because, as a rule, they are equipped with tips. I am sure that Sennheiser did this for a reason, out of nothing to do or to stand out from the competition. Another surprising thing is why only the Germans thought of this? 
Once again I admire the Sennheiser engineers and give them a standing ovation 
Chinese companies definitely have a lot to learn from them 
I think those who live in England understand me very well ^^
So yeah, metal shells are "very durable and reliable shells"! 
In addition, if the metal is also polished to a mirror state, as is the case with the FiiO FD5, then micro-scratches will inevitably and very quickly appear on the shells. Even with short, extremely careful and exclusively home use of earphones 
After about 9 months of intensive use of the Sennheiser IE 300, nothing happened to them either (although their bodies are also entirely made of plastic) 
Plastic can also be different — good and bad, cheap and expensive. This is not to mention the different implementation of the body itself, made of plastic. Therefore, everything is relative and far from being as simple and unambiguous as you describe 
