A Copper Toby from 7g up to 20g is one of the best lures out there imo. I have cleaned up with them on Garry nad Awe for pike over the years. They are also very effective at attracting Ferox but I find the larger fish aren't as keen on them as fish in the 2-4 bracket.
I add an extra split ring at each end and use Kamazan chemically sharpened trebles with mine. I'm a flat line troller and I always set my clutch tighter when trolling tobies and I've no problems.
Another option is to add an axtra treble on a short piece of fuse wire just off the top split ring. Haven't tried it myself but no a troller who does and swears by it and says the action of the lure isn't changed by it.
I haven't considered the single hook option as I've had no need to but the longer shank would certainly give less potential for leverage and unhooking.