I currently have a set of disc brakes with shimano 485 callipers and 525 levers. Would the 2013 SLX 675 callipers be a worthwhile upgrade?
Are you asking about the caliper to go with your M525 levers or complete brake?
If just the caliper, why not get a complete Deore M596 brake?
Nice as M675 calipers are, it will be expensive for you to upgrade with your current M525 levers. You need a banjo type hose for the M675 caliper (BH90) in addition to the caliper, as your current calipers have a straight hose, and can't be used
For the cost (and probably a lot less) of the hose and caliper, you can get a pre-bled complete M596 brake.
Would be just the calliper as a friend is selling a pair. For the hassle I think it would be a lot easier to just upgrade to a whole "set"