I've had a 510 Bartleby for a while now, but until now I've been using 901 adapters on it. I finally bought some 510 attys to see what all the fuss was about. BIG difference. It's a little harsh if you let it run dry, but this thing really produces vapor... AND throat hit. I'll probably still use my 901 for some juices, but I have to admit after almost 6 months of vaping... I'm impressed. I'm really surprised I could be surprised, but I am! Methinks I'll try to recess one of these in a 2AA box... perfect compactness!