Floating shelves - who has experience?

With shelf supports, it was said that the board does not lie flush against the wall and "wobbles".

If the board is properly milled and drilled, nothing wobbles. And if the board does not lie flush everywhere, it might also be due to the wall not being straight ;-)

I had finished boards with the supports on the wall for years (from Hülsta), they hold firmly - but they were also worked on precisely. An amateur with "cheap tools" might not do it so perfectly and then be unhappy.