So my quick story with Karis:
I had read the Nexy President's rubber design history posts and was intrigued by Karis. When BH Man hinted it had arrived and he had stock, I order a couple in the harder sponge, M+. I used T80 on a Yasaka Extra (I have 4 or 5 of those YE blades) so I put Karis on to test. The first night, it played and blocked reasonably well, though my teammates for the Butterfly teams were worried that I Was testing rubbers so close to the teams. I played league matches with it and performed at my usual level, noting that the rubber was just less bouncy than T80 but had a very direct feeling - no easy spin like T80, no extra curve or arc like T80, but good spin and good control which I could use to adjust the power and the brush. So I ordered M to compare to M+ and I found that I played at least a well if not better with M. So I decided pretty quickly that I would be using Karis at the Butterfly Teams. Again, at the Butterfly Teams, I played at my usual level with it. The one thing I noted was that I had a lot more control with Karis, because it was much less bouncy than T80, which was a good thing. What it helped me realize was that I could probably use a faster blade than the Yasaka Extra with the Karis because I wasn't trying to negate the bounciness of my rubber with a slower blade any more.
So I tested Karis M+ on an Innerforce ALC. The next day, I struggled with dead balls in some matches at the league, but managed to beat a player in the league who I hadn't beaten in over a year and who is just hard to beat (someone actually congratulated me today for beating him, just to show you how hard it is). I then played some matches with other players in my club and I realized that while I could hit more powerful balls with M+ than M, the difference was marginal and that I was often much more consistent with the M. I then used both interchangeably but out the M on a classic Primorac wood. I used the M and the Primorac to beat a kid who I haven't beaten in tournament play in almost 3 years.
So what about the Karis M/M+ do I think helps? Consider that I Switched to an IF ALC + Karis M+ instead of a YE + T80 and one of my opponents said I had gone to a slower blade. That just shows you how much control the Karis has. I can push short, push long, push dead. The topsheet grip is topnotch and doesn't slip so I can counterloop without stressing out over whether the sheet will hold up or not. And the lack of bounciness and the control it gives just encourages me to learn how to do other things with my game.
Does this mean that this rubber is better than Tenergy? Who cares. It's really about what this rubber does for your game. The point is that you aren't going to get easy spin on short movements with this rubber. But if you have good technique, you will get good spin with sharp movements and you will be able to control the trajectory of larger movements better. It blocks very well and the topsheet feels hard, even on the M, so it takes some work to make the topsheet work. But if you have that technique, then it is easier to control for a lot of strokes than faster rubbers that react to shorter movements are. Which is the point that the Nexy CEO was making - high grip topsheets out of harmony with the sponge often sometimes lead to the ball being excessively pulled in a direction other than the direction of the stroke on harder shots. KAris generally as a compromise for not being as easy to spin with, tends to spin and hit the ball in more intuitively linear way.