Kumho Solus KR21 - Tires NOT recommended(my opinion)

FYI.

Purchased and install 4 new Kumho Solus KR21 tires like 2 to 2.5 years ago.

Few months ago, I experienced vibration at low speeds(30-35mps) on one of the left tires - had to replace the structs, come to find out that, the specific tire was slightly out of shape and got it replaced and rotated(add to rear)
2 months ago, had another experience with vibration - got an alighment done since it was about 2 to 2.5yrs since the prior one and that didn't fix the issue - had to replace the tire and rotated(add to rear)
Now, am experiencing another low level vibration and based on what the mechanic is saying, one of the tires has inner threads broken so they are suggesting replacing the front 2 tires replaced ASAP

Also, found out that KR21 is discontinued and no longer manufactured.