I have now used the Bluegrip J1 in competition as well, plus 3-4 weeks of training (summer training so 6-8 hours a week) with it before the tournament.
It is a rubber that really suits my style, but I think it won't suit majority of styles.
To give more context, I am a left-hander attacker who relies heavily on a good and deceptive service and third ball attack, I like the short game and as soon as the game opens up I look to end it. On open game I can variate with the backhand, the forehand will only hit strong topspins, and if the other player manages to attack before me will be used almost exclusively for countering.
I use it on a DHS Long 5 (commercial version).
I will share my experience with it in competition, comparing it with a K3.
Disclaimer: I did not boost it, and I have a very strong sensation that this rubber is made for boosting.
- The rubber is and feels hard, much harder than the K3 I was using before; it also has much less catapult and it's more difficult to engage the sponge; it is more direct. Halfway between a K3 and a chinese boosted rubber I think (it is not as sticky as chinese rubbers tho).
- It shines in service and receive, where it has tons of spin and control for me.
- It has tons of spin in topspin game too, a bit more than K3.
- On opening topspins on backspin balls it needs good legs and precise technique with well used legs and body, it is much less forgiving than a K3, and on any gear from 1 to 5 it is harder to activate it. On gear 6 (so a 95 - 100% all-out forehand) I think it is faster and harder to block for the opponent.
- It needs a very fast arm and wrist, if you doubt your shot or are out of place it will feel like a brick wall.
- It really shines on counters too, be it on the table with a short movement or in positions 2 and 3 (medium distance and far distance) I felt like I couldn't go wrong with it. It has less exit than K3 (that I also really liked for countering) but if I hit it well I felt like I could ignore the opponent's spin and override it with mine.
I played with it in a round-robin tournament in England where I was the best of 9 players.
Of the other 8 players, 2 were closer to my level (right-handed attackers both of them), while the other 6 were on a considerably lower level.
1st match I didn't really try the rubber as the gap in level was too big with the opponent.
2nd match I played against a classic defender with long pimple (with sponge) on backhand. Defenders are my favorite style to play against and his level is considerably lower than mine. I lost the first two sets as I had a hard time adjusting to how hard the rubber felt trying a first strong topspin against a backspin ball, even having trained with it for three weeks, because my arm was not relaxed enough for it. Then I won the next three sets comfortably, adjusting and changing the game by moving him around and not trying to crush the ball anymore.
From the 3rd match I gained confidence, I was up against a right-handed attacker closer to my level and I started playing well and it lasted for the rest of the group, the j1 on my forehand remains very demanding on technique and legs but it was also very rewarding once the arm was relaxed and I committed to every forehand with my legs too.
Final disclaimer: I will keep on using J1 on the forehand, but I would not use it if I wasn't able to have good training sessions for at least 4 times a week starting from September.