They say necessity is the mother of invention, but I'd wager laziness is a pretty strong motivator as well. At first, attaching a Ben-Hur spike to the rear wheels seems like a pretty clever idea, but we can't help but feel like the thing is one step away from disaster the whole time.
Actually, that's a pretty old concept. IIRC, you can still buy these. I know for a fact they're all over Craigslist. as far as safety is concerned, yea, it's a bit intimidating, but employ a little common sense and you'll keep all your limbs. An old-timer neighbor of mine, long deceased, used to use one of these all the time. It was pretty cool to watch and was incredibly effective. Old school yankee engineering at its best.
I find stuff like this awesome. Its unmarketable, very useful, and hell...fun in a demented sort of way. No "WARNING" labels like on Chainsaws telling you to NOT stop the chain with your *****.... All 100% run off of common sense.
Then again I work at tractor shows doing stuff like this for fun.