Having driven a 2017 FiST with the symposer intact for over 90K miles, I would say the most annoying thing about it is the "BBUURRrr" whenever I roll into the throttle even a little bit. When having someone commuting with me, it can be almost embarrassing. Trying to accelerate enough to show off how torquey the little booger can be to a passenger, but not trying to be obvious about it is virtually impossibly without the "BBBUURrr" from the dashboard giving away that you're getting into the throttle,...just a little. Come on man!
I now drive a 2019 with Thermal R&D 3" catback and COBB air intake. Those upgades, though a lot more expensive than the free stock symposer (LOL), give much better noises, and the sound is correlated so much more with the throttle. The Thermal R&D is quiet enough in the cabin that I think the symposer actually out blasted it, so the delete was necessary to hear the exhaust. I am so much more satisfied with the real noises of the actual intake and exhaust notes and the increased aggressiveness of the audial experience perfectly corresponds to the throttle input.
If you prefer to keep everything stock, then keep the symposer for the aesthetic experience of hearing something when you drive more aggressively. However, IMO, you'd be happier with a mild exhaust note that can be heard because you've trashed the rubber flap.
On another "note" (pun intended), a decent sounding exhaust can be had for less than $250. On my 2017 I had the resonator deleted by a local muffler shop ($70). After driving for several months, it seemed to settle into a pleasing, though quiet, throatier sound (hardly noticeable inside the cabin with windows up). The resonator pulls out lower frequencies and cancels out some of the burbbles. I later added a Borla muffler in place of the stock can ($180) and it woke up the exhaust even more. It added enough volume to hear the burbbles and exhaust sounds without being too drony. At that point, I could hear more in the cabin and deleting the symposer became necessary to enjoy the subtle exhaust enhancements over the "BBBUURrr".