I have used these tips for over a year with no problems at all. I have one on my Tascarella playing cue since last March and it hasn't glazed over, changed shape, or caused miscues. Again, I rarely hit with both high speed and extreme english (14.1 and 8-Ball) but my experience is that these are some of the best tips ever made, and I have used the Mooris and Kamui reg extensively.
IMO, most miscues are stroke-related, not caused by tip properties.
I'm going to echo this post. I'm playing with a Kamui black hard (for about 6 months now) and have had no glazing over problems. My only issue with the tip is that it's the hardest leather tip I've played with. I have triangles on my other cue and shafts and they're much softer.
Being the cheapskate that I am, I won't be replacing this tip for a long time. At the rate it's wearing, it's probably going to be the longest I've had a tip on a cue for years. When I do replace it I'll be going back to Triangles. The Kamui was ok, but for the price I'll stick with Triangle.