I absolutely hated how every Diamond table I ever played on in the last 15 years reacted when a ball hit the rail. (Pre-Rail modifications). Keep that in mind so that you know I am biased as you read my post.
I was able to play on a 9' ProAM Diamond at Conyers, GA about a month ago. This table was a few years old, but Mark Gregory modified the rails using RKC's technique, so that they are the same as the "Blue Label" tables. The cloth was well worn when I played on it, probably 4 or 5 months old. Simonis 860. The cushions were the Artemis, not the other Diamond cushions, because they had the clearly visible rounded nose on them.
I specifically went to this room to try out the rails. I shot a lot of 2, 3, and 4 rail position shots, along with 1, 2, 3, and 4 rail banks. Then I played one hole with a guy for maybe 3 hours.
The rails definitely did NOT play like a GC. Some shots did, and others did not. I thought the cueball still came off the rail faster than a GC, but it was slower than the prior Diamond design. At the tail end of a 3 or 4 rail position shot, the cueball just seemed strange to me. Again, my reference is a GC.
I will say I liked the rails a lot better than the previous Diamond rails I played on over the years.
At this point, the best description I can give is that the rails played more like a 3 cushion table than a GC pool table. Whether that is good or not I don't know. I really need more time on the table to decide that for myself.
My conclusion is I'm not decided if I like the rails or not. I need more time on the table (I haven't' been back there yet). I'm holding off on my opinion until I do that.