Well I am on day 5 with the same 2 510 cartos rotating and no problems with them. Defintely the way to go IMO. I fill them both in the morning before going to work. A single cart lasts me 4-6 hours of freewill vaping at work. Switch to an atty or drip at home with my pints in the evening. Yesterday, my battery died before the carto did! I use about 20-25 drops to fill using the condom method on the mouth piece, clean the cart with a Kleenex, then spin it in my hand. I blow threw the mouth end to verify it's clear. Put it on my SD and vape away. I tried them on HV @ 5V and found the vapor to be to hot for my liking. Also measured the resistance @ 2.8ohms on the carto and 2.4ohms on my 510 attys.