Maybe iStick 30W is a better match with Nautilus Mini than iStick 20W

If you are a beginner turning to electronic cigarette for smoking cessation, the Nautilus Mini is strongly suggested because this tank has no high requirement of high power output and still you can get the good flavour from the e-juice. If you still are seeking the similar taste as smoking cigarette,  increasing the power output is not advisable and maybe you can increase the nicotine content in juice to give you the throat hit. Anyway, the Nautilus Mini is a fine tank to start with and its small size will be preferred. Moreover, the iStick 30W over the iStick 20W is a good match with Nautilus Mini in case you want to upgrade to something with a sub ohm coil later on because iStick 30W supports sub ohming. When you are experienced enough, you can replace the old one with a sub ohm coil to enjoy the huge vapor production. But it's a pity that only two available coils(1.8ohm and 1.6ohm) are for the Nautilus Mini. However, you still can retain the iStick 30W to match with other sub ohm tank without purchasing another box mod, saving a lot of money.