I'm not reading through everyone's responses, but if it disorients as well would be nice. Like the UMP.
I think Supersonic works the best (maybe decrease mouse sensitivity too? idk how you'd go about coding that tho) [I'm honestly just thinking a more balanced version of Winter Houl when I imagine this in action] . Total Silence, like Jack pointed out, works very similarly as the disguiser according to our rules, and you the disguiser lasts the whole round with a toggle, so this item wouldn't be worth it in comparison.
Total Silence and Disruption seem like perfect options so help make this weapon viable. Good Job Opalium!