I can personally vouch for the ZT 0550, it is simply a great knife all around to me. It looks good, good F&F, tough as nails, and, despite what else you may see, there is generally nothing wrong with the detent, as it is stiff at first but breaks in nicely. Of course, you can always find one where it is not perfect, as with any brand or model.
I have never owned a Horseman, but have had a couple of other Emerson models, and I think overall they are fine knives as well. The F&F on my CQC-7V is fine. Are there marks on the liners? Yes. Does it bother me even on a knife at "this price point?" No. Would it bother me on a full custom with a big price tag? Probably. But it doesn't affect the utility, performance or function of the knife, nor does it, at least for me, mar the appearance. Listen to the others who actual have and/or have handled the Horseman for its feel and performance, but don't be put off by generalizations that, at the end of the day, are inaccurate of the brand overall for either one. And good advice above of looking on the exchange for either - you can find some good deals on knives that have been well-cared for and in excellent condition. Good hunting.