I finally finished this! The first of my 64 string designs that I've actually made. I uploaded a photo with it next to a typical 16 string bracelet. It was difficult to keep the large diamond motifs straight due to the number of strings. The zigzags on the sides were easier to keep sharp. I also erred in making the triangle start too tight, so it was hard to get the first diamond shaped well. It took about 30 hours total, with about 7,500 double knots. The time was reduced a lot due to the side zigzag sections being quick to make. The diamonds and the dense interior designs were painstaking. I had to replace about 20 strings. I made variation #319576. Overall I would say my satisfaction with the result is about 6/10. I think I will try a 48 string design next, see if it's easier to get it really square.
I am 50% of the way through making this, with two large diamonds almost complete and one more to add. Overall it is proving hard to get really square shapes and straight lines, just due to so many strings, but the pattern is not very difficult to follow. I expect to replace about half the strings by the time I finish so I'm getting a chance to improve my skills there. It does make a big difference how carefully and well you do it.