Is it your first catback for the fiesta or did you change over from another one? I'm looking at one myself, but am slightly worried about drone as I do drive longer distances on occasion
My experience -- Stock, FSWERKS, Thermal R&D, Tune+ with rear silencer... the Tune+ sounds great, it's deep mellow, best workmanship of any I've seem by far, lightweight, proper 2.5" tubing, excellent service from Adam (really, over the top), excelent value for the money, and many are happy with it. It does, however resonate-drone at 3,000 to 3,400rpm with moderate to max load, more than I like.
The FSWERKS is much quieter and enjoyable for a relaxed drive with passengers (Installing this from the 2014 car to the 2018 car before I sell it), the Thermal I haven't had much time with other than warm up and leak checks on the car, and a little seat time to see how I like the sound, but it's well documented and discussed. I have a full Tune+ for sale by the way for anyone interested in stopping by the house for a good deal. About the light weight... weight reduction is an awesome tool to improve acceleration and braking performance, and grip and handling next if done in the right places. My car responds well to adding weight down low in autocross, many back and forth experiments with this, so I went with a heavier system, opposite of what others do.