My experience with the Kizuna K63 premium is largely positive. Have been playing with this string for the past 2 months, 8 to 10 sessions so far. I string my racquet at 27lbs mains and 29lbs crosses, with a 10% pre-stretch, 2 pieces 4 knots. Strings didn’t snap but have the usual signs of fraying.
Feel and sound:
If I were do compare it with yonex strings, I’ll rate it as medium feeling (slightly softer feeling than Ultimax). Produces a nice ‘boom’ during smashes and nice pinging sound on net shots due to the thin guage.
Pre-stretching the string does help with the retaining the tension for a longer time. The playability of the strings definitely lasts longer than ultimax.