Flush / wall-aligned interior doors - experiences?

What providers for flush interior doors with concealed frame and good price-performance ratio can you recommend?

This sounds like a trick question to me, because firstly, for a luxury product the price-performance ratio works almost inversely to that of basic necessity products due to competitive pressure and therefore can only be "relative" at best; and secondly, this market segment also has strong "social control," meaning a provider can neither afford outrageous rudeness nor major screw-ups. I see the issue arising right where your question is imprecise: "flush" with what (a plastered or tiled masonry or drywall wall, wood paneling, ...)? And does "concealed" mean the invisibility of the frame only from the room side or (like what?) also from the hallway side and/or even the lining side? I hope you can understand why your question sounds as if a self-declared wine novice is ordering the "finest tipple" that the waiter can serve.

I hope you can understand why your question sounds as if a proven wine novice is ordering the "finest drop" the waiter can offer.

Thank you for your answer. It is about the interest in a flush interior door with a hidden frame on one side of the door. It is clear that this is an expensive version of a door, but that is why we are asking for recommendations for dealers. Unfortunately, there are also expensive doors with poor quality. That is why I am asking you for recommendations. Thank you very much!

What providers for flush interior doors with hidden frames and a good price/performance ratio can you recommend?

None. We had also briefly considered that. My wife knows such doors from her office and fell in love with the look. However, the topic was dead after a relatively short research because the prices are quite high. A carpenter explained to me that on the one hand, extremely precise work is required in construction, and on the other hand, the fittings must be of the highest quality so that the gaps are harmonious and precise – and remain so. The question is roughly like asking for a cost-effective but high-performance Formula 1 race car. :) We filed that under "dreams only millionaires can afford."

We have recorded that under "Dreams only millionaires can afford."

That's how it is. That’s what makes the question about an affordable Rolls and Cartier dealer so amusing.

I was then explained by a carpenter that, on the one hand, construction has to be extremely precise and, on the other hand, the fittings must be of the highest quality so that the gap dimensions are harmonious and precise – and remain so.

And that's why it makes a world of difference whether the interior fitter delivering the doors is the same one doing the wall paneling. And vice versa, the idea of separately procuring the doors is so much a candidate for the Hall of Blame. In this sense, your answer

It is about the interest in a flush interior door with a hidden frame on one side of the door.

unfortunately remained imprecise to a critical extent.

P.S.: I am currently reading your other question

We are currently planning a storey extension on a house with many glass fronts and are looking for a modern solution for the exterior facade. For example, we find Trespa facade panels very attractive.

and from this I gather that it is about an existing building into which the entire area must fit. Usually, you can still fill out an extra voucher for realizing such luxury details. Incidentally, I strongly recommend that you start a separate overall project thread in which you present the building with the usual synoptic plans current/target/extension.