Once I rented a 26 foot moving truck. Before he would give me the keys the guy went through the paper work and spent a few minutes telling me to use the mirrors and to signal when changing lanes, to be aware of the truck's length, to brake early enough to allow for the truck to stop, etc. All really obvious stuff. I nodded politely and said "so, basically, you are saying don't be stupid."
If you think these products really need a warning label then I'd make it something simple like "Attention : Don't be stupid."
"Pleases the whole family... A new thrilling recreation as you beautify your lawn." I would want one even more if it were powered by an actual rocket.
5 pounds of cyanide for only 3 bucks. Cheaper and probably easier than using your Rocket Mower to take out a squirrel. But why not use something a bit more personal like the Aeroil burner :
With a 2000º F, 30 inch flame you can use it to destroy weeds. The ad specifically recommends it to kill weeds, seeds and roots, disinfect poultry and livestock quarters and claims 99 uses.
Note that the farmer is wearing both a hat and tie as he uses his mini flame thrower.
Also note that it was sold out of New Jersey, a place that now bans fireworks (even sparklers) and requires a BB gun to be regulated as a firearm (despite a BB gun's complete lack of fire)