From what I understand, the Heavy Tow has less HP gain because the more you increase the HP, the higher and faster your EGT's tend to rise under heavy load. Because of this they keep the Heavy Town tune slightly better than stock for max GVW towing. The Light Town tune is for lighter loads to your discretion. As long as you have a monitor you can decide which is best suited for your needs.
So I have been through a few different exhaust setups now.
1. Flo Pro 5" with straight through "glass packed" muffler. This had good throaty sound under acceleration and is mild through town, however had it had the most hi way drone around 110km to 120km of the three setups. but is definitely in the middle for volume of sound in all other applications.
2. Flo Pro 5" straight pipe. Sounds great and is is really loud under acceleration and still managed to stay quiet while cruising through town. Hi way drone actually seemed to be slightly quieter around 110km to 120km than the glass packed muffler setup which is interesting. I do feel that if you were towing with the straight pipe that the drone would probably be quite loud as it does ramp up as you go up hills and the boost starts to increase slightly, then goes away at the top of the hill.
3. Flo Pro 5" with the 5" Twister. Flo Pro recommends the Twister be installed as close to the downpipe as possible so there was a bit of things I had to do in order to do so. The 5" exhausts for these L5P's is actually a 4" intermediate pipe from the downpipe to just in front of the torsion key crossmember, there is also quite a few bends in there. I ended up placing the muffler delete pipe from Flo Pro in place of the muffler, then placing the Twister immediately before it which gets it directly under the back passer seat foot well. As far as sound goes, it quiets it down ALOT. The drone at 110km to 120km is still there but you have to mute the music to hear it, there is no issue speaking at a normal tone in the cab to passengers. Driving around town I would compare its volume to driving a stock mustang 5.0... its there but not crazy, almost too quiet if you like some noise. Under acceleration its similar to the muffler setup but I would still stay its quieter, by far the most tame set up. I personally really liked both the muffler and the straight pipe setup, but my wife appreciates the Twister so I guess the decision has been made for me haha.
Keep in mind I have a 2020 with a 10 speed.. the drone may differ with the 6 speeds.
I have been in contact with my tuner in regards to this. They have been dealing with HP Tuners quite closely and have even been part of the BETA team for the original tunes and SOTF tuning. It sounds like it is an operating system problem with the ECM's themselves and there hasn't been any direct relation to it being SOTF related. That being said, HP Tuners is making some slight revisions in both the Single tunes and SOTF tunes and will be releasing updates soon for all who are interested, you would just have to contact your tuner. The place I got mine done at has only had 1 customer come back with a failed ECM and it was with a Single tune. They are going to be sending me updated tunes in the coming weeks once HP Tuners releases them. I will keep you posted.
Overall, I am not to concerned. It's like anything else, some guys have injector issues, electronics issues, etc... and some don't. Guess we will have to wait and see who is lucky and who is not lol.