I don't see many reviews for this new J6 tyre so I'll add my comments.

I had experience with previous J5 on a friend's Myvi with size 175/65R14. Tyre is approx 2 years old.
Comfort and quietness is pretty good. Very similar to previous experience with Mich XM2 and Conti CC6
Dry and wet grip for daily use is very acceptable, didn't really get to push the car since it's a Myvi not a sports car.

This got me interested to try the new J6 on my own Myvi G3
Just got it fitted earlier this week, size 185/60R15

Stock Myvi G3 size is 185/55R15. Decided to up the tyre height due to firm suspension on the Myvi G3 which became unbearable.

First impressions (less than 100km):
Fairly quiet and very comfortable. Very similar to XM2/CC6
Dry grip is good.
Wet grip will test when I get to.

Will report back with further findings in a few months time.
Edit:
In case you're wondering,
XM2 is good for quiet and comfort and it's a very good well rounded tyre for daily use but it's too pricey especially for popular tyre sizes.
CC6 quiet and comfort is excellent but the dry grip is average and the wet grip is really quite bad.

For myvi G3 stock tyre is Goodyear Assurance Triplemax. Grip on this tyre is very good but compound is hard. Not comfortable and very noisy. The J6 and with +5 in profile height transformed the car. Much more livable daily now.
Update 1 Sept 2021 (Tyres ~3 weeks old / 800km mileage):
It's been rainy season the past few weeks.
- Wet grip is good
- Wet braking is acceptable. Myvi brakes suck but the tyres do help.
- Dry braking is good too

Update 17 April 2021 (Tyres ~6 months old / 5000km mileage):
- Still performs as well as new
- Tried same size Michelin XM2 on a friend's car, noticed J6 sidewall seems a tad softer than XM2
- I noticed that the XM2 has slightly better grip in dry compared to J6. Probably due to the stiffer sidewall on XM2
- Comfort and noise on the J6 does seem slightly better than XM2 (based on my own un-scientific judgement the J6 probably ~10% better)
- Also found out recently that the Dunlop J6 has increased in price. Becoming more popular recently or due to inflation? I don't know

Update 29 August 2022 (Tyres 1 year old / 10,000km mileage):
- Still performs as well as new
- Tyre noise is slightly increased when pressure is low (e.g. -40kPa from recommended). Pump air pressure back to manufacturer recommended pressure and its quiet again
- It's not as dead silent as when new, but still relatively quiet (+10% noise compared to when new)

Update 17 April 2023 (Tyres 1yr 8mths old / approx. 15,000km mileage):
- Comfort: Still good
- Noise: Not as quiet as before, still very OK (+30% noise compared to when new)
- Dry grip & Dry braking: Still performs fine under aggressive driving
- Wet grip: Not so good and not very confidence inspiring. Still better than CC6 but with similar age the XM2 definitely outperforms J6 in the wet.
- Wet braking: Stopping distance nowhere as good as when new. Tyre tends to slightly skid/slide when harsh braking in wet (you shouldn't be driving like this in the wet anyway)
- Thread depth: Yet to rotate my tyres but the front threads still looks really new (front wheel drive car)

Update 7 Dec 2023 (Tyres 2yr 5mths old / approx. 22,000km mileage):
- Comfort: Still good
- Noise: Not as quiet as before, still very OK (+30% noise compared to when new)
- Dry grip & Dry braking: Still performs fine under aggressive driving
- Wet grip / Wet braking: Noticeably not as confidence inspiring in the wet
- Thread depth: Yet to rotate my tyres. Front threads look like they've been worn in about 50% at the moment.
Will be rotating my tyres front-back during upcoming service. Definitely won't be doing any aggressive driving in the wet from here on.