I’ve used Rotos starting back in 1972. They’re one of my goto string sets. And I’ve nearly always had a set installed on a least one bass since then. And if I had to characterize Rotosound 66 steels, this is how I’d describe them: First up, I’ve never had a set keep what I think of as ‘zing’ for four months. My experience is that their super hot new string fizziness disappears about three or four hours after being loaded. Which is fine by me because I consider a set of Rotosounds straight out of the package to be almost unusable for what I’ll be playing. After that some of the sharp steel roundwound edge (zing?) still hangs in. But it gradually diminishes over a week or so of playing before settling into what I think of as the characteristic Rotosound signature vibe. Which to me is bright and piano like, but still very controlled and focused. Depending on how much and hard you play, that signature sound can last anywhere from one to four months after that. Beyond a little over four or so months, when on my bass they start sounding very much (to me) like a fairly new set of GHS Pressurewounds. At which point I’ll usually replace them. But in any event I hardly ever keep them on past the half year mark anymore. Please note this is just my impression based on what my ears hear and how I play. So don’t take the above as anything other than just one longtime player’s opinions.