I've got the 61" Frontier 4-in-1 on my JD3720, and it's been an absolute lifesaver. But only after considerable practice. But six months later, I can pick up just about anything bigger than a golf ball. I put a toothbar on mine, which extends the versatility even more. With that, I can actually putt the golf ball. A pile of brush? No problem. I can also pick up a bucket full of rip-rap now. Never found an effective way to do that with a 5' standard bucket on a compact tractor. I've grabbed/torn broken limbs outa trees, picked up whole trees and carried them to the brush pile, even grabbed a few rolls of fence wire (one at a time of course).
Seeing as how I bought it new, it was comparatively expensive. But I now truly convinced that it's well worth the money. If you can get one in good condition for a grand, go for it. But understand that your tractor will have to have three pair of remotes (lift-lower/curl-uncurl/open-close) and an extra controller to open/close the jaws.
//greg//