diamondback:
- reward is given instantly for no sacrifice
- gun has minor penalties when used without crits (damage nerf that is shared with other popular meta revolvers like letranger and amby, but 6 shots per reload is retained)
- you absolutely can get 2 shots off quick on a player and insta drop them if you time it right
frontier justice:
- if your sentry gets kills in order to provide you with crits, you have to actively either kill your gun or allow your gun to BE killed in order to receive your reward
- gun without crits is functionally a zero-miss endeavor as with 3 shots if you miss at all on most classes you just dont even have enough ammo to compensate for your mistake
also in 6s you dont want to use the diamondback anyway because the unbanned meta alternative the l'etranger gives such a massive passive buff of having more cloak to have a better time getting in position