The Horizon C and D are similar in appearance, but a bit different in feel and action.
shoegazer
is
spot on about the detent on closing the C. I'm about ready to file a ramp on mine, as the action would be perfect otherwise. I've had a Hills for a while, and yes - SMKW flash sales are
wallet killers. They had the Hills for an incredible price a while back. As well as the Torrent, Epoch, Future, Horizon D... The C is an incredibly solid knife, and I'd compare the solidity to my ZT 0392. Just bigger and heavier.
Mine is black with gold standoffs and clip, I paid about $200. I can also recommend the Hills, it almost feels like it's assisted when opening, I love the size and full flat grind. Then again, I haven't met a Reate I don't like, which is why I have far too many! Check Nick's review above, Epic Snuggle Bunny (Austin) also did a review of the C. Anyway, it's a good place to start, but proceed with caution as you would trying heroin!!
[edit] The Hills is available at KO for $180, so it really boils down to your size preference. The C is more substantial/fit & finish in every way, I carry my Hills far more often (beat the crap out of it TBH), YMMV.
http://knifeoutlet.com/Knives-N-to-Z/Reate-Knives/Reate-Hills-Folder