I've got a Merlin 4 MB (in A3kD) - it's running fairly well, but I can't actually recommend it (only when it's cheap).
True and High Color resolution is rather limited due to the ET4000W32 design, and there are quite a few design problems since the card was released before the design was completely finished.
There's only a Rev V3.1, AFAIK no other revs exist.
German page of developer
