My guess on the Arrow pipes bulge is that it's a solution that more closely mimicks the converter to eliminate tuning issues. The limitation that piggyback tuners have is that they have defined blocks and values of adjustment, at least all the ones I've fooled with. So say the factory exhaust setup requires a lean spot or bump in timing at a defined spot in the map due to it's design, then you change the exhaust (or any other hypothetical mod) that changes the dynamics so that lean spot/ timing bump is no longer required, it now needs a smooth fuel curve in that spot. So with a cracked or directly tunable ECM you can do exactly what you need but with a piggyback tuner you can only adjust the area contained in that particular cell by a positive or nagative value, so your basically taking a predefined segment containing the lean Spike and moving the entire thing toward the rich side which fixes part of it but makes other parts richer than they should be. Now it's not some massive section of the map in each cell but it can create difficulties, flat spots/hesitations in some situations that can't be entirely fixed. And that's all considering your in closed loop running off the map directly. Hopefully that makes sense... Open loop using the ECM's "auto tune" is a little different. I contacted Bren tuning to see if the 790 was on their radar and they said it wasn't but that they may look into it. They did offer flash tunes for the 1290. They are a top notch tuner, I had their tune in my 1299 and it turned a very refined bike into near perfection.