Having a quick look, it seems very mixed with some people getting one and others not, sounds like a propper remap can sort it out
*EFII chopped my centre silencer and got the flat spot as you say, now i've got the Scorpion resonated system and the Toyo manifold and the flat spot has all but gone (but could still do with a remap)
Regardless of what you have though, a remap is probably 90% guaranteed to fix it. RSTuning or EngineDynamics are the lads to go to for remaps on these cars.
They are about 45 minutes away from me and I have been tempted to get mine done. Let me know if you feel any difference!
I thought the gains Vs cost of this was minimal and pointless, money better spent else where