Thornless blackberries are fabulous ! I've got one that's at least 15 years old; it was mature when we moved in, so no idea how long ago the previous owners planted it. It still produces masses of new vines every year, if anything the problem is keeping it trained and under control.
It might be an age thing, but I've found that when it roots itself the new vines from the fresh root can sometimes be spiky. Likewise new plants that grow from any blackberries that drop onto the ground and grow. The birds drop quite a few all around the garden, so a job every spring and autumn is to go round and find them all so we don't wake up one day with an impenetrable mass of brambles 😁
RE: The thornless blackberry vines are really coming along