F.I. All the way! I own both exhausts. Originally bought the Ark V2 Grip and I can tell you that you can't beat the performance or the sound of FI.
BTW they have the best customer service hands down. Most companies are only nice to you pre-purchase or during the sale but once you get after purchase support they suck or don't reply if you have issues.
FI will help you every step of the way.
