Npro is my 1st vaping device. It was cheap @ $20. But the refills were $15 & they do not last very long. After some testing I found that the cartos from 21st Century actually fit & they produce more vapor. I got a disposable 21st Century from Circle K for $10. You can pop the top and refill this cart or use the cap method. This is working for me right now while I save up.