The ubass strings are an improvement over the silicon ashbory strings, but if you want immediate tuning stability you're not gonna get it. It takes literally months for ubass strings to stabilize, but once you get there, it's a wonderful thing. There are other string options such as Aquila thunderguts and silver rumblers, but many people find them sticky and squeaky.
I had a Acoustic U bass and now own a SB fretless Ubass. It will take several weeks into a few months for the U bass strings to stabilize so play it as much as you can. I'm considering going back to an acoustic model for different reasons.
Mine took several months to stabilize, and now is good. After playing a few songs on stage when I check the tuning it is always a little bit sharp. I retune and play a few songs and its a bit sharp again. I’m used to it and check my tuning often.