Yes, I have also heard many times that the Elpro is fine.
During the time it was available, I was too slow, and so I missed it.
I use a lens produced by B+W (NL5), which has a diameter of 77 mm, and a 77-69 mm step-down ring produced by Heliopan. Although looking a bit bulky, this combination does its job quite well, and there are no problems in the corners due to the larger diameter of the added lens.
Of course, "pixel peepers" will find some faint chromatic abberations in the images, nevertheless, I am pretty satisfied with the general quality.
Best regards, Peter.