Getting a secondary device is a wise move, old vaping adage of backups for your backups so you are never stuck without a vape, especially with your short vaping journey thus far. Yes a variable adjusted device will work best in any scenario, depending on your wattage will determine basically your nicotine level, example going sub-ohm from standard ohm vaping (generally higher watts from the get go) most will step down to 1/2 their previous nicotine level. Due most times you are double the watts you are still basically getting the same nic per vape exposure, higher watts produces more vapor, more vapor = more nic exposure per volume, or close to it. Just remember, with an replaceable battery mod, consider what wattage you will be running will narrow down the list of what battery/batteries you will need, and also remember you will need an external charger for those batteries, and battery X2 the number the mod uses to run, example single battery mod = 2 batteries needed minimum (one in use, one charged or charging), 2 battery mod = 4 batteries (2 in use, 2 charging or charged).
Suggested batteries
20amps (50 to 60 watts max per battery, single battery 50 to 60 watts or lower, dual battery 100 to 120watts max or lower, etc) = Samsung 30Q, Sony VTC6, or LG HG2 (all 3000mah and around 20amps).
25amps (65 to 75watts max per battery, single battery 65 to 75watts or lower, dual battery 130 to 150watts or below, etc), Sony VTC5A (take note of the "A") 2500 to 2600 mah, LG HD2, HD2C, or HD4 2000 to 2200mah, all 25amp batteries.
30amps (80 to 90watts max per battery, single battery 80 to 90 watts or lower, dual battery 160 to 180watts or lower), LG HB2, HB4, HB6 all 1500mah true 30amp, do not fall for marketing gimmicks of a battery saying on its wrapper and label 35 or higher amps, there is no battery in 18650 format that exceeds 30amps Continuous Discharge Rating (CDR), any that claim higher are a lie and a danger (what we call re-wrap companies and are dangerous batteries if you even try to reach these false amp ratings in a CDR situation, stay with the Big Manufacturers with 18650 batteries (LG, Samsung, Sony/Kinion, Sanyo/Panasonic <-- Everyone else buys from these guys any way, much safer and cheaper to stay with these Big 4).