Mags on Grapefruits?

Hey everyone, I'm apprenticing at a shop in Sacramento (Tattoo the Body Embellished), and the artists don't really use mags too often. I'm going to go get a tattoo by an artist in Roseville who's worked on me before so I can watch her technique a little... I've already started tattooing at the shop, done 7 so far, but only using rounds. I don't want to transition into mags yet because I know they can be more damaging to skin if not used properly. So I was wondering if it'd be useful to use mags on grapefruits? I asked the artists at my shop and they said it might not take too well on the fruit. Any experience with this? Thanks! -Jess