I'm under the impression that compression drivers (field coil or otherwise) vary less from best to worst than horns do.
According to Bill Woods and a few other sources I have encountered through reading, only a conical horn can deliver the original sound waves intact. Tractrix and elliptical designs cause cancellation within their bell which results in a distorted delivery. When you talk to Steve Schell, ask him about that.
After researching the various opinions I've heard, I'm pretty confident that Bill knows what he's talking about. Field coils likely will further sharpen what is already a phenomenally clear picture.
These horns may not be for everyone as they present a very focused and utterly unadulterated voice. I'm talking espresso black, straight whiskey, rifle barrel delivery. By comparison your cone drivers give you beer with milk in it.
Its weaker and murkier. I know you don't think so now and I imagine you will need a while to get used to good horns, but if you do, there will be no going back to the tame, diluted sound of big brand everyday, ho-hum, reviewer darlings.
I wish I could afford Bill's bass horns. Donations are welcome.