If I am going to be shooting nearly 100% suppressed, is there any advantage to one system or the other as far as just being a suppressor mount system from TBAC cans?
The sidewinder is simply the x-large version of the hellfire. For almost all suppressors, the hellfire is needed. The sidewinder is just too big to be adapted to 1.5” cans. If you're running a 338 ultra, the sidewinder is fine.
I run the hellfire system with my ultra 9. I’m not to terribly worried about having to use the warranty but you’ve asked a valid question and I wouldn’t mind knowing.
Area 419 voiding anything on any product would cause an uproar. The fact that the thread pattern in just about all cans are basically a standard says no it wont. Use whatever system you want. If they didn't want you to use another system, they would have made it a uncommon thread in the business.