Two new studies looking at whether electronic cigarettes help smokers to quit their deadly habit have found that while some of them can, it depends on the type and how often it is used.

The research suggests daily use of so-called “tank” e-cigarettes, designed to be refilled with nicotine-containing liquids, is most likely to help smokers quit. So-called “cigalike” e-cigarettes are disposable or use replaceable cartridges.

Researchers who conducted the two new studies, published in the journals Addiction and Nicotine & Tobacco, said they show that smokers wanting to use e-cigarettes to quit should use them daily and try “tanks” rather than “cigalikes.”