I´m pretty sure there was never a really dissatisfied Nicolai customer, ever.They seem to have periods where they radically change the design of their bikes, I'm highly skeptical that they actually keep hundreds of "parts", rather, they probably fabricate as needed, which puts you down a rabbit hole of "oh, we'll get to that in a few weeks...months...years". Saying it is one thing, delivering is another. No evidence that they don't, but extraordinary promises become suspect to me.
I mean, for a 10+ year old frame they most likely won´t get you a part shipped in 2 days, but they´ll get you one and imho, especially in this day and age, that counts for something. Apart from that, their stuff is built pretty damn tough. One can dislike their designs, but their build quality is most likely the best in the business. Never seen one fail either.
Compare that to Canyon for example who won´t even sell you a replacement part after 2 years after the warranty period expired or if you damaged something by your own fault, even though they have them in stock because they only have enough stock to handle any warranty claims. They do not even think about providing anything beyond what is their legal obligation. Happened to a friend (and many others) who was stuck with a frame without a chainstay. After 2 years.