I have already seen this thread about 1fichier, but I though maybe something has changed in the meantime, so I invested 3 EUR to give it a try.
So in case anyone is wondering, it still works exactly as described in the previous thread, i.e. there are very hard limits and due to forced delays the upload of a lot of small files is incredibly slow. I am getting speeds only about 1 or 2 % of what other hosters are able to achieve on my 30 MBit/s upload connection (Backblaze B2, Jottacloud).
However when testing large files, the situation is different and the upload happily runs at 100 %.
So for me with hundreds of thousands files I won't bother and will go through the Jottacloud route.