Expect 9,000 to 12,000 genuine draws, which is three weeks or so of average use. Boost or turbo modes, where fitted, roughly double the liquid used per puff, so the headline number assumes you leave them off.
The device carries two separate tanks and coils; a physical switch or twist selects which one the airflow runs through. Nothing mixes, so a menthol side stays clean next to a dessert side, and you can run the two down at different rates.
Only if the specific device appeals; the tiers overlap heavily in price. Pick by feature: the 15K shelf has the newest pod systems, while 18K owns the flavour-switch gimmick that many people genuinely love.