I have these on my Salsa Casseroll. They're pretty good.
Fit and finish are excellent, just below Shimano. I found some machining marks on one of the calipers and the polish isn't quite on par with Shimano (but then again, neither is the price).
Braking power is excellent - but these brakes are a touch mushy compared to other brakes I've used (Paul Touring, Shimano BR-R550, Shimano Ultegra).
My front R556 had a sticky mechanism out-of-the-box. I cleaned and oiled the pivot and that fixed the problem.
Overall - I would buy them again. But if I had the cash, would go for the Shimano large-capacity sidepull.
On an LHT, I would skip sidepulls and go for Paul Neo-Retros or Touring cantis. These make all the other brakes I've ever used seem inferior by comparison.