I'm not sure if Foxhunter if referring to lunging with 2 lines, or ground driving, or (what's the real difference anyway), but I love it. You don't need to stick to circles, but you can, and can reverse them with contact which is great so they really follow through. You can keep the feel of the horses mouth and control their back end. I like to go over poles when ground diving. I use a plain halter with my horse, a surcingle and 2 lunge lines.
On a few occasions I've also used the side reins while ground driving but looking back I don't think it was necessary or accomplished anything special with the combo.