[This post has been sitting in my drafts for months.]
I got my flatwounds, and I'm in love. I liked them from the moment I peaked into the package the moment when I got them. The thread color is purple, and it only has thread at the top, which seems so old school [to my utterly uneducated mind]. They feel like silk, I want to keep running my hand over the strings [more the the feeling then the sound, like the rotos].
The roundwounds bite when you change strings, flatwounds don't and I could play them for hours for the feeling. The rotos sounded zingy with the G string sounding down right like a piano. In contrast the flats sound almost woody, dull in a warm way, mellow.
I'd probably go mad if all my basses only had flatwounds, but I like having one pass with them, it's calm, plus you can't beat the investment since flats last for years.