The XtremeMac FS1 was a revamp of Future Sonics' old EM3 (or "Ears") product. Basically the same driver, but with a newer, prettier casing. Later, Future Sonics used that casing design as the basis for the Atrio, which has a significantly updated driver. So no, the FS1 is not a clone of the Atrio, it's the precursor to it.
I have never tried the FS1 directly, but I own both the EM3 (which is basically an uglier, utilitarian FS1) and the Atrio. The Atrio beats the EM3 in every respect. Better soundstage, better high end detail, no more treble roll-off, etc. One might think that (after the Atrio has burned-in) the bass response might not seem as great as in the EM3, but that's more because the Atrio's bass is more controlled. Pop in some hip-hop, or A Perfect Circle's "Thirteenth Step", and the Atrio will show you just how much massive bass response it's capable of (quite impressive, honestly).
But yes, the FS1 one is/was MADE by Future Sonics, and marketed by XtremeMac. I'm sure their fine, and I'd take them over any Shure or Etymotics IEMs any day (I find those other brands too fatiguing and bright), but I really do prefer the Atrio in every respect. The Atrio is all I use now.