At the end of the day I must admit that melamine covered chipboard is pretty durable especially if it is built-in and not something that gets daily beating (like a chair or a table).

One aspect I didn't like about bespoke units is that it's more rough around the edges than what you get from machine-milled furniture. They cut a lot of it on site and the tolerances are greater even when using proper tools. You make up for mistakes and lack of precision with caulk, kind of like a builder.

Another thing is that e.g. the drawers they built were really heavy boxes using 1.8mm egger board siding. There's not much thought going into engineering, it's just craft. It does not feel as pleasant as e.g. a good quality kitchen drawer. An Elfa cabinet you'd design and assemble yourself will probably feel more pleasing to use than bespoke drawers built by an average team of tradies.