I second that. I've had the fuel mod in for a couple of weeks now but idle (12 o'clock) waiting for my dna filters to arrive (stzge 1 and 2).
Filters arrived yesterday, put them in this morning and the bike is so much smoother. I already had the O2 mod, which helped make the standard bike a lot better and following the advice on this forum is really doing wonders.
Shame the standard 660xt needs mods though.