Is there a lot of tension on it as it flips back and forth, requiring high leverage as you flip it?
In a word, yes. Did you see how he released tension on the apparatus? He rotated the barrel log towards the load allowing the rope to unwind. That's the purpose of the stakes, to prevent that from happening under load. If you placed your lever pole in the center you could only crank it one time, not terribly useful. The method is ingenious but I'd add a few suggestions. Use low stretch, high strength rope such as dacron. Synthetic line snap back is no joke. Many sailors have been maimed or killed when large nylon (read; elastic) anchor or tow lines parted (broke, snapped) under load. Dacron has far less stretch but still be aware. The best approach is to remain well clear of the load line under tension but this set up requires one to be right in the danger zone. Anything draped over the lines under tension would absorb most of the force if it parts under load. I've used heavy blankets or coats but in this case a floor mat draped over the lines on both sides of the winch mechanism would be a wise precaution. And very important, new rope will have a Working Load Limit (WLL) that is some fraction of its breaking strength. A 5000lb vehicle rolling freely on wheels could be moved easily with a smaller rope but that same vehicle mired in mud may require many times that amount of force to free it. And what condition is your rope? Damaged, dirty, or frayed rope will have less breaking strength than new. I always err on the side of caution when sizing my rigging.
