Are internal gutters problematic?

The downpipes are not particularly nice, but also not an insult to the eye.

The plain wall surfaces, for which they even hide downpipes where the eye finds nothing, are an insult to the eye. Today's builders seem to find that great, I dread it.

It is absolutely no problem if done correctly.
We have welded smooth pipes with leak testing...

If you have very deep pockets, you can basically build almost anything that gravity allows.
In traditionally insulated houses, mold and cracks often occur in the area of the overly insulated downpipes – depending on how this was constructed.

They are not sitting in the insulation with us either.
Feasible even with a smaller budget.

Visually, this creates a very clean line. We like it very much. I do not see an insult to the eye there. Although I am a cameraman. However, we would of course place a much greater value on durability. The downspouts are only planned in protruding walls that support the roof overhang. See photo. I could imagine that these are not connected to the direct building envelope and therefore might not pose a problem from an energy perspective. The argument about the water and heating pipes actually seems very understandable to me. It would be interesting to know if anyone has had any concrete bad experiences with this.

We have welded smooth pipe with leak testing….

That means the pipe is one piece along the entire length?

The downpipes are only planned in projecting walls that support the roof overhang. See photo. I could imagine that these are not connected to the direct building envelope and therefore might not pose a problem from an energy perspective.

So you actually only meant the downpipes? No, you are right, they don’t disturb the thermal envelope at this point.

It would be interesting whether someone has already had very concrete bad experiences here.

I assumed that you meant (at least also) internal eaves, and for those I attribute (speculatively) the fashionable short lifespan besides constructive particularities to operational, maintenance, and repair practical reasons. I have been around since 1980 already for quite a while, and I specifically remember from this trend intensively that it was a flash in the pan. Even the knee-break roof windows lasted longer.

If there are several pieces, they should be as long as possible and welded with the Geberit system. Then everything is closed up and pressurized… The second step is actually not necessary because there is a welding monitoring system.