Never had flatwounds, and this seemed like an inexpensive way to try them. And it is. First couple of hours is getting used to the texture, different feel of glide and pressure, fingers "stick" to them fair bit more than on rounds, but seems like it gets less with use.
Completely different feeling and sound, I think these improved sound of the HB JP-550OP which has that motown-ish (Aria Detroit?) vibe anyway, but only now it is complete. Very positive experience, these will stay on it for a long time (they say flats last for years) and I will buy a jazz for other types of sound.
Packaging is nice with strings individually packed, and as a bonus, red silk ends on both sides give fancy looks :)