I was starting to get discouraged because the cartridges all tasted like burnt plastic, cleaning cartos sounded like a chore, and topping off constantly was a real bummer. Then a fellow vaper told me about the Riva-T which fits on my Riva 510. Heaven. Nice clean taste, easy to fill, and attractive price wise. Just ordered three more from cropduster 901 and had a nice chat with Tony (yes, spoke to an actual person). He was very helpful. Know this might not be the answer for everyone, but for a beginner like me it made the whole process a lot simpler. Won't swear that I'll never upgrade, but am very happy for now.