Yes, grinders are great at cutting things, principle design function if I'm not mistaken, I'm fairly sure an airsaw won't just bounce off flesh if you get in the way........they just stop quicker, but can still give a decent hack. Plus the thing is physically awkward to use in the confined space.
People need to take some responsibility for their actions, I suggested what worked perfectly fine for me as I'm not a complete retard and treat tools with respect, and if I've not used one before I'd get someone who is skilled at using it to do the job. Hence why if someone posted "the best way to do the job is on a lathe" I wouldn't be running out to give it a crack, as I have NFI how to use one and would end up getting clocked by a solid piece of metal.
Personally I'd be more concerned about him using a stanley knife to cut the soft foam, they don't know when to stop and so many people have bad technique it's not funny.
I gave him the easy rat and peanut butter option....