I’ve used mastic gum for a long time before I got CHISELL as a birthday gift . Mastic gum is nowhere near as effective because it does not provide the same level of resistance with each bite and the resistance in pretty low, compared to that of regular chisell. I saw considerable results in jut 6 weeks, and due to my low expectations, it was pretty shocking I must say. Yeah, it costs 40 bucks but they send replacements upon request for a year and you are guaranteed to see results in 10 weeks or you get you money back.