I have tried many different Vpes. My favourite is the Pebble, unfortunately it stops working for no reason within 3wks rougjly. I have recently purchased the etank, the piece you place into your mouth is metal, I don't like that and I found it choking when inhaling. Ironically, I find the epen the best, the only problem verses the Pebble, the bit you place in your mouth you don't throw away unlike the Pebble, and have to clean it everyday.