I use these strings for half a year and they almost sound like in January, when I got them.
Ernie Ball of course is, in my opinion, one of the best manufactures of strings in the world. But nevertheless they are expensive. On the other hand when you compare these strings with other strings, 25 ? is a OK. Because bass strings are expensive anyway.
The sound of the Ernie Ball Hybrid Slinky strings is very good and crisp, and I really love the open sound. And these strings are sustainable; because after a half year they sound almost the same. My, of course quite cheap bass, sounds much better since I use these strings. I had never believed before, that strings can make a so big difference in sound quality.