How long does one can last?

Depends on how much you crack the lid and your cabin size, but most drivers get several weeks to a month out of an 80g can before the scent fades noticeably. You'll know when it's time to swap it out.

Will this work in cup holders or do I need a vent clip?

The round can fits standard cup holders without any additional hardware. You can also set it on the dashboard or in door pockets—no mount required.

Is the jasmine scent strong enough to cover odors, or more of a light refresh?

It's a light refresh. If your cabin already has heavy odors, this will layer over them rather than mask them completely. Best for cars that are already clean and just need a pleasant scent boost.