These are simply the best bass strings I've ever used. I have 3 bass guitars, an active schecter, a fender Jass and a precision 'copy' I made myself and I've used a variety of strings over the years and these stay in tune better than any of the others that I've used. The winding seems to be smaller, giving them more mass and so a better sound. The schecter, which doesn't get used very often has had the same strings on for a few years now, and mine have not tarnished at all.
When I started on bass I made the mistake of using cheap strings the main problem was that each string had a different volume as the weights and mass was not very well balanced. That's easy to sort on a guitar by adjusting the screws in the pickups, but much harder to do on a bass, but the slinky were a good matched weight and I don't get that problem. I think good strings are the cheapest way to improve your sound.