I use to use the Co2 oil cartridges in A o.pen 5 volt battery charging pen for a short period of time. I liked the convenience , portability and how discrete it was but I had so many problems with the battery not working properly and the oil cartridges also malfunctioned. The high when I first stared using them them was amazing , clean and long lasting euphoria...but after about 6 weeks I wasn't getting high at all and just got really bad headaches. I used the so called pure co2 extract thinking it would be the healthiest. I have talked to a number of people who seem to have the same problems as myself with the high...at first great then nothing but a headache..kinda strange.