Stun-gun salesmen may use the argument that video recording schemes actually prevent abusive behaviour by law enforcement officers.
Watch the video linked here [LINK].
I think that YouTube's business model is safe. Even with cameras rolling, some police are still going to be stupid.
If the salesmen claim that video recording equipment will prevent such stupidity, they're just being salesmen.
Free advice: Lease, don't buy. Make sure there's an escape clause. Don't lock yourself into any long term contracts. Make them earn your money every day. Or don't bother.