Well, when I bought my Jazz, they installed the Fender CL flats (the much sought-after 45s to 105s) on it, and I played with them for about 3 months. I knew flats need time to break in, and I was trying to break them in. They did sound like flatwounds, but they had a bit of zing to them I didn't like, and which the tone control didn't really take care of. Foam muting them helped a little with the zing, but I felt it never really gave me a lot of bottom end. I will say that the tone seemed more consistent on all four strings off the bat (or out of the package) than most other flats I've tried, including my favourites (which I won't repeat here because, well, half of my posts are about singing their praises) but the tone really wasn't doing much for me on my particular Jazz bass (which is a VM 70s lefty).
They were also doing a number on my neck, turning it into a sling. I guess they had a lot of tension or something, and they did feel stiff on my particular bass. The lovely setup job they had done for me was slowing going to poop thanks to these strings.
I ended up giving these strings to a fellow lefty bassist, who was contemplating selling his MiM Jazz. He decided to give it another go with these strings, and promptly fell in love with the sound. I checked back with him recently, and asked how he liked the sound, and he said they ended up sounding a lot better after some more break-in time.
TBH, I'm beginning to wonder how they would have sounded on one of my P-basses I have no acquired or built since. How I rate them? Well, depends on which bass I will try them on. The flats I currently have on both my VM Jazz and newest bass are not making me want anything else for the time being, but I suppose somewhere down the line, I might give them another shot.